Dozens of tornadoes tore through parts of Oklahoma, Kansas, Nebraska and Iowa overnight and one twister killed at least five people.
The storms struck what is often called ‘Tornado Alley’ in the US Central and Southern Plains and more were forecast.
But casualties appeared limited because many of the twisters hit sparsely populated areas, and during daylight hours or evening when people were still awake.
In Oklahoma, a twister struck the northwest city of Woodward early today morning after lightning apparently disabled its storm warning system, Mayor Roscoe Hill said.
Two children died at the Hide A Way mobile home park on the west side of Woodward, a town of 12,000 people, while two adults were killed in a small community just outside the city limits, Mr Hill said.
Details of the fifth death were not immediately known, according to Keli Cain, spokeswoman for Oklahoma Emergency Management.
"This thing took us by surprise," Hill said, adding storm sirens had not sounded. "It's kind of overwhelming".
Mr Hill said he was told the tornado hit the west and north sides of the city, badly damaging an apartment complex where residents were trapped and awaiting rescue.
A tornado that struck Woodward in April 1947 still ranks as the deadliest in Oklahoma history, with 116 people killed, according to the National Weather Service.
In Kansas, a twister also churned through parts of the state's second-largest city of Wichita. Storm chaser Brandon Redmond, a meteorologist with the Severe Weather Alert Team, said the twister passed over his vehicle and lifted it two feet (60 cm) off the ground in an industrial area south of the city.
"The tornado literally formed over our vehicle," he said. "I've never been that scared in my life. ... We had power flashes all around us and debris circulating all around the vehicle, sheet metal, parts of a roof, plywood".
Damage was reported to a mobile home park, and Mr Redmond said there was significant damage in the industrial area on the city's south side.
There were no immediate reports of injuries. Residents in the affected Plains states and in a wide area of the middle of the US stretching from Minnesota to Texas hunkered down for more severe weather.
The National Weather Service said the worst conditions were expected in Oklahoma, Nebraska and Kansas, while other areas could see baseball-sized hail and strong winds.
"Conditions will remain very favourable ... for very strong and potentially long-lived tornadoes," the National Weather Service said in an advisory.
It warned that night-time tornadoes could be particularly dangerous because they are usually fast-moving and often obscured by rain and darkness.
Reuters