President Joe Biden declared a state of "natural disaster" and released federal reinforcements to support areas affected by "storm, flooding, landslides and mudslides".
Torrential rains battered eastern Kentucky overnight Wednesday through Thursday, turning some roads into rivers and forcing residents to take shelter on the roofs of their homes while waiting for help.
Others have been trapped by rising waters or swept away in their vehicles, and the toll is "appalling", Governor Andy Beshear said.
“We now have 16 confirmed deaths, and this number will still grow considerably,” said the elected Democrat at a press conference.
Four brothers and sisters, aged between one and a half and eight years old, were swept away by the waters when they had taken refuge at the top of a tree with their parents. The bodies of two of them have been found and two remain missing, according to the local newspaper Lexington Herald Leader.
The parents "had managed to hold their children for a few hours but a big wave came and took them all at once," their cousin Brittany Trejo told the daily.
An 82-year-old woman also drowned while trying to get to safety, authorities said.
In the most affected places, houses were submerged, the lightest torn from the ground. "Hundreds of people have lost everything" and it will take at least a year to rebuild, said Andy Beshear.
In the meantime, the emergency services, supported by reinforcements sent by neighboring states, are all mobilized to come to the aid of the victims.
About 50 air rescues, with National Guard helicopters, and hundreds of boat rescues have already taken place, according to the governor.
"But there is so much water, the currents are so strong that we cannot reach everyone," he lamented.
Heavy rain is expected until Friday evening, and the flood alert has been maintained.
- Tornadoes -
With human-induced global warming, the atmosphere contains more water vapour, increasing the chances of heavy rainfall events, scientists say. These rains, associated with other factors linked in particular to land development, promote flooding.
Some areas of Kentucky received some 20 centimeters of rain in 24 hours and, in places, the waters of the rivers suddenly rose several meters before emerging from their beds.
In the Jackson area, some roads have become mighty streams, with abandoned cars here and there.
Below these small valleys surrounded by forests, the land was flooded with light brown muddy water that in some places only allowed the roofs of buildings and trees to protrude.
Thousands of people remained without electricity or running water on Friday. Shelters have been opened in gymnasiums, churches and state parks.
"These are the worst floods in Kentucky's history and they come after the worst tornadoes in Kentucky history," Andy Beshear said.
In December, several dozen violent tornadoes ravaged five states in the center of the United States, mainly Kentucky, and killed at least 79 people.
President Joe Biden, who went there, then pointed out that the weather phenomena were "more intense" with global warming.
