Image source, WA POLICE

A four-year-old girl missing for 18 days in a remote part of Western Australia has been found alive and well in a locked house, police have said.

Cleo Smith disappeared from her family's tent at a campsite near the town of Carnarvon on 16 October, triggering a massive search effort.

Police smashed their way into a locked house in Carnarvon at 01:00 local time, where they found her.

A man from Carnarvon is in custody and being questioned by detectives.

"A police team broke their way into a locked house… They found little Cleo in one of the rooms," Western Australian Deputy Commissioner Col Blanch said in a statement on Wednesday.

"One of the officers picked her up into his arms and asked her 'What's your name?' She said 'My name is Cleo'," he added.

The four-year-old has now been reunited with her parents, who had made desperate and emotional pleas for Cleo's return since she vanished.

"Our family is whole again," Ellie Smith, Cleo's mother wrote on Instagram.

Police, who had offered a A$1m ($750,000; £540,000) reward for information on Cleo's whereabouts, have not given more details on the man in custody.

"We'll have more to say on the rescue of Cleo as the day unfolds," Deputy Commissioner Blanch said.

Image source, ABCImage caption, Extra police officers were deployed to the area from Perth

Australian PM Scott Morrison, who is currently in Scotland for the COP26 climate summit, tweeted that it was "wonderful, relieving news".

Cleo's family were on the first night of their holiday at the Quobba Blowholes camping ground when she went missing between 01:30 and 06:00 on 16 October.

The remote site in Macleod is about 900km (560 miles) north of Perth, and is a local attraction on the state's Coral Coast – known for its windswept ocean scenery, sea caves and lagoons.

Cleo had been sleeping on an air mattress next to her younger sister's cot. When her mother, who had been sleeping in the second room of the tent, got up in the morning, Cleo was gone and the tent door was open.

The mysterious disappearance sparked an extensive air, land and sea search, with extra police resources sent to the site from the state's capital city, Perth.

The case drew international attention, and there were reports that bounty hunters had travelled to the region to join the search once the cash reward had been offered.

News that Cleo has been found alive and well sparked a sense of huge relief in the local community.

Carnarvon Shire president Eddie Smith told Australia's 2GB radio: "For 18 days we've been filled with anxiety and concern. I'm a bit emotional at the moment."

Ben Fordham, the radio host interviewing Mr Smith, broke down while reading the police statement on his show.