“Some people’s houses were completely swept away in the middle of the night while they were sleeping,” the governor said.

Hundreds of people had been rescued by boat and there had been about 50 aerial rescues using National Guard helicopters, he said.

With many roads washed out “we still can’t get to a lot of people,” the governor said.

“The current is so strong it’s not safe for some of those water rescues that we need to do.”

Eastern Kentucky has had flash flooding previously “but we’ve never seen something like this,” Beshear said.

“Folks who deal with this for a living, who have been doing it for 20 years, have never seen water this high.”

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Some areas of the state’s Appalachia region reported receiving more than eight inches (20cm) of rain in a 24-hour period.

The water level of the North Fork of the Kentucky River at Whitesburg rose to a staggering 6.1 metres (20ft) within hours, well above its previous record of 48.2 metres (14.7ft).

Many roads resembled rivers, mangled cars littered the landscape and muddy brown floodwaters lapped against the rooftops of low-lying houses.

Kayla Brown, 29, and Joe Salley Jnr, 56, residents of Perry County, told the Lexington Herald-Leader newspaper that the fast-rising floodwaters trapped them in their mobile home.

“It was like a wave coming at you out of the ocean,” Salley said.

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Neighbours came to their rescue after their trailer was knocked off its foundations.

Four young children ranging in age from 18 months to 8 years old were swept away from their parents in hard-hit Knott County, the Lexington Herald-Leader reported.

Brittany Trejo, the siblings’ cousin, told the newspaper the bodies of two of the children had been found, but the other two were still missing.

Their parents were rescued after clinging to a tree for eight hours, Trejo told the Herald-Leader.

“They managed to get to a tree and … held the children a few hours before a big tide came and washed them all away,” Trejo said.

The eastern Kentucky flooding is the latest in a series of extreme weather events that scientists say are an unmistakable sign of climate change.

Nearly 60 people were killed in Western Kentucky by a tornado in December 2021.

The National Weather Service warned that more heavy rain was expected on Friday.

US President Joe Biden issued a disaster declaration for Kentucky, allowing federal aid to supplement state and local recovery efforts.

Deanne Criswell, head of the Federal Emergency Management Agency, arrived in Kentucky on Friday to tour flood-hit areas and report back to the president.