Violent thunderstorms and tornadoes lashed the U.S. Southeast and mid-Atlantic region on Wednesday, killing at least four people in Virginia a day after twisters claimed three lives along the Gulf Coast, authorities said.

The National Weather Service (NWS) warned of tornado activity along a line of storms stretching from Raleigh, N.C., north to parts of Virginia, Maryland and the Washington, D.C. area.

"We're swamped with tornadoes on the ground here," said Weather Service forecaster Brandon Dunston in Raleigh.

Three people were confirmed dead in Waverly, Va., a town of some 2,300 residents about 70 kilometres southeast of Richmond, the state capital, where at least three structures sustained heavy damage in a mid-afternoon storm, state police spokeswoman Corinne Geller said.

State police later said the three victims - two men, aged 50 and 26, and a two-year-old boy, were killed when their mobile home was demolished in the storm. Their bodies were all found about 300 metres from the trailer site, police said.

The body of a fourth person, an adult male, was recovered late on Wednesday in the Evergreen community of Appomattox County, near Lynchburg, after a funnel cloud was reported over the area, police said.

Witnesses told The Associated Press the storm swept through Waverly with little warning.

Timothy Williams said a friend had just come by to take his new car for a drive when the storm hit.

"It picked the car right off the ground, and put it right back on the ground," said Williams, 44. He said they remained in the car until the storm passed.

The storm blew down electrical wires "in a big ball of fire, thrashing all about each other," Williams said. He said they both escaped shaken but uninjured.

"I'm just a little nervous and jittery, but overall I'm OK," Williams said.

South Severe Weather Virginia

Lightning lights up the night sky behind a home in Waverly, Va. on Wednesday night. (odd Spencer/ The Virginian-Pilot via AP)

Two highways leading into Waverly, U.S. Route 460 and State Route 40, were left impassable by heavy debris from the storm, state police said. Authorities also were responding to widespread reports of local flooding.

Virginia state police reported severe storm damage and numerous injuries in the riverfront Essex County town of Tappahannock, northeast of Richmond, and in Appomattox County.

Richmond station WWBT-TV reported more than 20 people injured in Tappahannock, some possibly trapped in storm wreckage. And seven people were hurt, two seriously, in the Evergreen community, state police said.

Tornado watches were posted through much of Virginia, and Governor Terry McAuliffe declared a state of emergency to hasten delivery of disaster relief to stricken areas.

Schools cancelled in several states

A storm earlier on Wednesday destroyed a mobile home in Wayne County in central North Carolina and wind gusts of up to 85 kilometres per hour were reported at the Columbia Metropolitan Airport in South Carolina, the NWS said.

Just north of Oxford, N.C., near the Virginia border, high winds damaged several houses, one of them blown "completely apart," Granville County Sheriff Brindell Wilkins said, adding that power outages were widespread. He said a number of people suffered minor injuries.

Schools in North Carolina, South Carolina, Georgia and Florida canceled classes or shifted hours ahead of severe weather forecasts.

South Severe Weather Virginia

Tornado damage along Richmond Highway in Appomattox County is shown on Wednesday. A funnel cloud left an 12-to-15-kilometre path of destruction in the country. (News & Daily Advance via AP)

Wednesday's severe weather came as rescue teams combed through debris left by several tornadoes that pummeled southern Louisiana and Mississippi on Tuesday, claiming at least three lives and injuring dozens more.

Among the hardest hit was the Mississippi River hamlet of Convent, Louisiana, about 95 kilometres west of New Orleans, where a mobile home park was largely demolished. In neighbouring Assumption Parish, more than 100 homes and businesses were damaged and several were destroyed, authorities said.

Florida Governor Rick Scott declared a state of emergency for two counties lashed by a tornado on Tuesday night. Several people were injured and about 70 homes damaged when a tornado ripped through Pensacola, Fla., local media reported.