Devastating flooding in Kentucky killed 25 people and the toll is expected to rise, the southern US state's governor said Saturday as rescuers continued their search for survivors.

Torrential rain earlier this week caused unprecedented flash flooding in eastern Kentucky, a region hard-hit by poverty.

"We've got some tough news to share out of Eastern Kentucky today, where we are still in the search and rescue phase. Our death toll has risen to 25 lost, and that number is likely to increase," tweeted Governor Andy Beshear, who had previously put the death toll at 16.

"To everyone in Eastern Kentucky, we are going to be there for you today and in the weeks, months and years ahead. We will get through this together," he added.

Beshear previously said hundreds of people had been rescued by boat since the flooding began Wednesday evening, while National Guard helicopters carried out dozens of aerial rescues.

Some areas reported receiving more than eight inches (20 centimeters) of rain in a 24-hour period.

The water level of the North Fork of the Kentucky River at Whitesburg rose to a staggering 20 feet within hours, well above its previous record of 14.7 feet.

The flooding turned many roads into rivers, and some houses in low-lying areas were almost completely submerged, with just their rooftops visible.

The weather offered a respite on Saturday, but more rain was expected the following day.

"As a cold front drags south, the area will remain mainly dry through today. The dry weather is expected to come to an end Sunday afternoon as a boundary lifts north back into the region," the National Weather Service's Jackson, Kentucky office tweeted.

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.

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