A massive tornado killed at least nine people and flattened almost all of a small town in Kansas on Friday.
More than 60 people were injured when the tornado - said to be up to a mile wide - hit the town of Greensburg.
More than 95% of the 1,500-population town was destroyed, including the hospital and schools as well as homes, local officials said.
A new wave of tornadoes hit southwest Kansas on Saturday evening, affecting at least six counties.
The National Weather Service forecast the development of strong tornadoes in central Kansas and Nebraska during Saturday night.
Earlier, a tornado in central Nebraska damaged buildings and power lines, officials said.
Greensburg, around 120 miles (200km) west of Wichita in southern Kansas, received a direct hit by the tornado late on Friday.
The tornado was described as a "wedge", a particularly wide formation carrying winds of up to 250mph (400km/h).
Storm chaser Darin Brunin told CNN that the tornado appeared to be at least a mile in diameter.
"A big tornado like that, that moves slower, it can tend to do a lot more damage because it's over an area for a longer amount of time," he said.
Residents said warning sirens went off 20 minutes before the tornado struck, giving them a chance to get to storm shelters.
The storm ripped homes from their foundations and even damaged basement shelters.
"You could hear the top half of our house start tearing up," one man said.
"We were under a bed in the basement. We were just fine, but windows were breaking and smashing."
One of the few buildings still standing is the courthouse. The city hall, schools, businesses as well as homes were destroyed.
At least eight people died in Kiowa County, where Greensburg is located, and one in the neighbouring Pratt County, a spokeswoman for the Kansas Adjutant General's Department said.
Sharon Watson said officials were looking into reports of two further storm-related deaths in the area.
Rescuers spent Saturday combing through the wreckage for both victims and survivors.
Thirty survivors were reportedly pulled from the rubble of the town's partially-collapsed hospital.
Residents were evacuated and the National Guard brought in to provide security.
"This is a huge catastrophe for this small town," City Administrator Steve Hewitt told a news conference.
"My home's gone, my staff's homes are gone."
"We've got to find a way to get this to work and come to work every day and get this thing back on its feet. It's going to be tough."
Mr Hewitt estimated that 95% of the town had been destroyed and warned that it could take days for rescuers to reach survivors trapped in basements and under rubble.
He warned the death toll could rise.
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