At least two people was killed and more than 30 were injured following an explosion at a chemical plant in the German city of Leverkusen, just north of Cologne, on Tuesday.

Authorities initially issued an “extreme threat” warning and told residents to stay indoors following the blast at a facility for processing chemical waste. Several people are still missing. 

People were urged to take shelter and keep their windows closed as warning sirens sounded and a thick plume of smoke spread over the city. Motorways in the area were also closed for several hours.

"My thoughts are with the injured and with loved ones," said Chempark chief Lars Friedrich. "We are still searching for the missing people, but hopes of finding them alive are fading."

Police said five of the 31 injured people were affected seriously enough to need intensive care.

A cloud of dark smoke rises above the Chempark facility in Leverkusen

Credit: Mirko Wolf/DPA/AP

Mr Friedrich said it was not clear what had caused the explosion, which led to a fire starting in a tank containing solvents.

"Solvents were burned during the incident, and we do not know precisely what substances were released," Friedrich added. "We are examining this with authorities, taking samples."

Air quality tests by the environmental protection agency in the neighbouring city of Cologne in the early afternoon found there was no immediate danger to the population.

But drivers were advised to keep their windows closed and switch off their air conditioning as a precaution.

The explosion took place at around 9.40am local time (8.40am BST) in a hazardous waste processing facility at Chempark, one of the largest chemical plants in Europe on the banks of the river Rhine.

Wegen der Explosion in Leverkusen sind Feuerwehr, Rettungskräfte und Polizei aktuell im Großeinsatz. Ausmaß und Schadenslage sind laut Polizei derzeit noch nicht bekannt. https://t.co/G8ag8mrswz pic.twitter.com/XrWsoahcFz

— WDR aktuell (@WDRaktuell) July 27, 2021

There were initial fears the ensuing fire could spread to other parts of the plant containing hazardous chemicals, including a 100,000-litre tank of highly flammable iron solution.

But firefighters were able to put out the blaze by early afternoon, according to the city council.

“The extinguishing work had to wait until a power line was disconnected from the grid,” a spokesman for the council said.