Human remains have been found in the rubble of a collapsed apartment block in Miami as hopes fade that the 159 people still missing will be found alive.

Miami-Dade Fire Rescue Assistant Fire Chief Ray Jadallah told a family briefing on Saturday evening: "It’s not necessarily that we are finding victims. We’re finding human remains."

The room, packed with dozens of desperate relatives burst into a collective gasp and a number of people could be heard crying.

"I am trying to locate your loved ones," he added.

The official death toll now stands at five, but Mr Jadallah said: "I have been asked for two days. I wanted to tell you the truth."

He added that authorities are working to allow family members to visit the site either on Sunday or Monday.

Mr Jadallah declined to say what or how many human remains have been found.

One family member said he wanted to "remove the trauma as soon as possible," and asked when the search and rescue mission would become a recovery mission.

"It’s never a specific time or factor. 9/11 went for months before it was a recovery. We are nowhere even close."

Two women comfort each other at the Surfside community centre

Credit: Jose A. Iglesias/Miami Herald via AP

Earlier rescuers say that “tapping sounds” detected under the rubble had dissipated but Mr Jadallah said sounds could still be heard.

The mood on the ground has soured and families are demanding answers after it was revealed that engineers found alarming evidence of “major structural damage” at the tower in 2018 that had not yet been addressed.

Search and rescue teams have been battling fires, torrential rain, falling debris and acrid smoke for three days, but have not found anyone alive since Thursday. Deep-rooted fires are hampering recovery efforts, officials said, adding that they are using infra-red technology to try and identify the source.

So far, four people are confirmed to have died. 120 people have been accounted for and 159 are still missing.

A pregnant British mother, her husband and their one-year-old daughter were staying at the Champlain Towers South building when it fell down three days ago, and the Foreign Office is supporting family members.

The first victim has been named as Stacie Fang, a 54-year-old events coordinator, who was pulled from the rubble alive, but succumbed to her injuries in hospital. Her 15-year-old son, Jonah, survived the collapse and was rescued by a member of the public who saw his hand sticking out of the debris.

Stacie Fang was identified as one of the four confirmed dead in the collapse

Credit: UNPIXS

On Saturday it emerged that a report written by a consultant in 2018 found “major structural damage” to the concrete slab below the pool deck and “abundant” cracking and crumbling of the columns, beams and walls of the parking garage.

The waterproofing below the pool deck was described as being "past its useful life" and should be replaced.

The 40-year-old building was supposed to undergo major renovations as part of a recertification process this year, but engineer Frank Morabito recommended that action be taken “in a timely fashion” three years ago.

The report, unearthed by the New York Times said that repairs were needed to “maintain the structural integrity” of the building and its 136 units.  Miami-Dade mayor Daniella Levine Cava said she had not seen it until this weekend.

The exact cause of the deadly incident is still not known, with subsistence, flooding, the activity of nearby building sites and the possibility that a sinkhole opened up beneath the apartment block all being examined.

Sources on the ground have told the Telegraph that they believe a sinkhole caused the centre of the building to cave in.

“Have you seen the pile of rubble? It’s not that high. Where did 12 stories of rubble go?” said one person with knowledge of the search and rescue mission.

A team of US government scientists and engineers has been flown to Miami to urgently assess whether the collapse should trigger a wider investigation that could change building regulations across the country.

Experts fear that other buildings could be vulnerable to catastrophic structural failure if they have been built in the same way or stand in a similar location.

The city of Miami’s building department has launched citywide inspections of all buildings six stories or taller that are 40 years or older. The audit will be completed within 30 days, Ms Levine Cava told reporters on Saturday.

Already, Surfside mayor Charles Burkett has requested the evacuation of Champlain Towers North – a building just one street away that was built at the same time, by the same developers, using the same materials.

“I don’t think that people need to live with the thought that their building might fall down,” he said.

Mayor of Surfside Charles Burkett hugs Rachel Spiegel, whose mother is missing

Credit: AP Photo/Lynne Sladky

On Saturday, rescuers said that “tapping sounds” that had been picked up by specialist sonar equipment at the collapse site has “dissipated.”

We haven’t really heard anything in a while now, but that’s not to say that there’s still not people trapped that are alive,” Dr. Howard Lieberman, a trauma surgeon with the Miami-Dade Fire Rescue task force told CNN.

“As time’s running out they might be getting a little more sick or ill, not as vocal as before, but, like I said, we’re going to keep searching.’”

Describing the scenes his teams were facing on the smouldering, smoky rubble, Dr Lieberman added: “We’re seeing stuffed animals, teddy bears, boxes of diapers, a child’s bunk bed, and we’re finding a lot of pictures, family pictures.”

Florida Governor Ron DeSantis said on Saturday: “You wake up in the morning hoping that people have been pulled out, but the news is not what we hoped.”

A “missing wall” has been set up on a nearby tennis court, with posters of loved ones that are unaccounted for. Dozens of bouquets of flowers have been laid down in tribute.

Rescuers continue to work tirelessly. 

“We’re not stopping until we’re done. We’re not stopping until everybody is pulled out of there,” said Mr Burkett.

Miami-Dade Fire Rescue chief Andy Alvarez told families of the missing to "have hope," and recalled that his team once pulled a girl out of earthquake debris in Haiti eight days into the rescue effort.

"You gotta have hope. We’re doing everything we can to bring your family member out alive," Alvarez said, pausing as he was overcome with emotion.

Rescue workers have worked around the clock in Miami

Credit: Gerald Herbert / AP 

What happened?

At about 1.30am on Thursday morning 55 of the Champlain Towers South building’s 136 units fell to the ground in a pile of rubble and twisted metal.

It took just 21 seconds for the 12-storey tower to collapse. The central section caved in first. The rest of the block fell on top of it.

The building was described as having “pancaked” – where one floor can’t support the weight of the one above and they fall through.

“It looks like a bomb went off, but we’re pretty sure a bomb didn’t go off," said Surfside mayor Charles Burkett.

The building, which faces onto Surfside Beach in Miami was built in 1981 and was popular with tourists, who rented out apartments.

Among the missing are people from Israel, Paraguay, Uruguay, Argentina and the UK.

What could have caused the collapse?

"There’s no reason for this building to go down like that unless someone literally pulls out the supports from underneath, or they get washed out, or there’s a sinkhole or something like that, because it just went down,” said Mr Burkett.

Sources on the ground have told the Telegraph that they believe a sinkhole opened up beneath the apartment block, causing the centre to cave in.

“Have you seen the pile of rubble? It’s not that high. Where did 12 stories of rubble go?” said one person with knowledge of the search and rescue mission.

According to a study led by Florida International University environment professor Shimon Wdowinski, which used satellite radar data, the site showed signs of land subsidence as far back as 30 years ago.

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"I don’t know if the collapse was predictable. But we did detect that the building moved in the 1990s," Mr Wdowinski told CNN on Friday.

"It’s very subtle. It’s two millimetres per year but it’s still detected by the satellites," he explained.

Matthys Levy, a consulting engineer and professor at Columbia University told USA Today that even the minor subsidence detected could have an impact.

"A millimetre may seem like a small number, but when you add them up over many years, it becomes a big number," Mr Levy said, pointing to the fact that one part of the building is still standing as potentially significant.

If one part of a building is well-founded and the other is not, he explained, it can cause distortion in the floor slabs and "suddenly, you get cracking, breaking and fracturing."

Rescue crew at the site after a partial building collapse in Surfside near Miami Beach

Credit: via Reuters

That can lead to what is called progressive collapse – as happened during the September 11 attacks in New York.

"If one part of the building fails, it drags the rest with it," Mr Levy said. "There’s nothing there to stop it, there’s no strong elements to hold it back. It’s a cascade."

Other theories have been put forward.

The building was about to be repaired for rusted steel and damaged concrete, according to a lawyer involved in the project.

Salt water from the sea can penetrate buildings and corrode steel elements. Sitting on the oceanfront for 40 years, the Champlain Towers South building has been exposed to hurricanes and flooding – both of which brought sea water onto the complex.

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Work on the building’s roof was underway, but experts have cautioned that this in itself is not likely to have caused the collapse.

There have been other complaints from residents. One filed a lawsuit over water intrusion that she blamed on poor maintenance.

Other residents have complained that nearby construction had sent rumbles through the structure, potentially unsettling the foundations, according to the New York Times.

What was the inspection process?

In 1992, Hurricane Andrew devastated swathes of south Miami coastline causing $34 billion in damage. 63,000 homes were destroyed and another 100,000 damage, with the hurricane exposing just how poorly many had been built.

As a result, new, much more rigorous building regulations were introduced designed to protect apartment blocks, houses and offices against extreme weather.

But the Champlain Towers South building went up in 1981. Old regulations meant that it was not due to be re-certified until this year.

People hang up signs of missing residents from the partial collapse in Surfside where the rescue personnel continue their search for victims

Credit: Reuters

Reacting to the collapse, and fearful of any more, the city of Miami’s building department announced on Friday that it will request citywide inspections of all buildings six stories or taller that are 40 years or older.

But some experts say the current inspection process isn’t deep enough, because it doesn’t account for the effects of sea level rise, floods and tides over the decades since older buildings were built.

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The majority of residential towers in Miami-Dade – 70.2 per cent – were built before 1990.

“Everyone associates Miami with beautiful glass and steel buildings,” David Haber, managing partner of Haber Law, a construction and real estate firm, told the Miami Herald.

“But we have a lot of concrete buildings just like the Champlain towers that are nearing the 40-year re-certification process.

“I’m getting condo boards asking me what they should be doing. Their residents are asking ‘Is my building safe?’ It’s the first logical question anyone living in those concrete buildings would ask.”

Will there be a full investigation?

"We need a definitive explanation for how this could have happened," Governor Ron DeSantis told a news conference.

"I do think it’s important that it’s timely," he added, "so that we get the answers to the families and that we get the answers to the people of Florida."

Atorod Azizinamini, chair of FIU’s civil and environmental engineering department, said structural engineers would collect vast quantities of data on the building’s design plans and construction methods.

They will take samples of steel and concrete, look at signs of corrosion, examine the foundation for signs of settlement, and try to detect any unusual event before the collapse.

Miami-Dade County Fire Rescue members search at the site of the Champlain Towers South Condo

Credit: Miami Herald

"Once we have all the information we can simulate exactly different scenarios, and we can pinpoint how the collapse took place," Mr Azizinamini said.

"Unfortunately that is not going to be happening in a matter of days, weeks."

"It’s going to take some time."

The federal scientists and engineers sent down to Miami have a different task.

National Institute of Standards and Technology spokeswoman Jennifer Huergo stressed that while this team is only looking to determine if an investigation will be recommended and not the cause of the collapse, it does have the power to subpoena and they will gather building materials that could be helpful if a full federal investigation is deemed necessary.

“If a full investigation or study is conducted,” the agency said in a statement, “its ultimate goal would be to determine the technical cause of the collapse and, if indicated, to recommend changes to building codes, standards and practices, or other appropriate actions to improve the structural safety of buildings.”

The team will not interfere with the search for 159 people who are still unaccounted for.