To see some of the devastation and some of the houses that just disappeared, it surprised me that we haven't had serious injuries

Robert Parsons, sheriff's deputy in Oklahoma

Despite the destruction to buildings, the authorities said only seven people had been injured, most by flying glass and debris.

Most of the damage was in western Oklahoma, but several tornadoes also caused destruction in central Nebraska late on Tuesday.

Some 12 tornadoes were reported in Oklahoma and 11 in Nebraska, said Weather Services Corporation meteorologist Dave Taylor.

They were caused by warm, moist air from the Gulf of Mexico mixed with a cold front and upper-level winds moving across the northern United States, he said.

Devastation

The town of Cordell, some 160 km west of Oklahoma City, bore the brunt of the damage.

A local official, Bob Lambert, said probably a quarter of all houses had been severely damaged or destroyed in this town of 3,000 people.

Windows were shattered, roofs were torn off homes, and trees and electrical wires littered the streets.

"To see some of the devastation and some of the houses that just disappeared, it surprised me that we haven't had serious injuries, much less fatalities," said Robert Parsons, a sheriff's deputy in Oklahoma's Washita County.

Mile-wide tornado

One Cordell man, Elmo Maddox, 72, climbed into the cellar of his daughter's farmhouse just seconds before the tornado hit.

"When we shut that cellar door, it was right on us," Mr Maddox told the Associated Press. "This was the worst I'd ever seen."

He described seeing two tornadoes merge into one system that seemed to be a mile wide.

Nebraska Emergency Management Service spokesman Tim Hergenrader said damage in the state was confined mostly to the three central counties of Polk, Merrick and Hamilton.

"You can't go anywhere at an angle here and find a farm that isn't damaged," Kent Adelson, who lives in Polk County, said.