Residents of the neighborhood surrounding Enterprise High School said they heard warning sirens long before the tornado slammed into the building, crushing the victims in an avalanche of concrete and metal.

"It came real fast, but they had plenty of time to get those kids out because sirens were going off all morning," said Pearl Green, whose 15-year-old niece attends the school and was hit in the head by a flying brick.

But school officials said they had no chance to evacuate earlier because of the approaching severe weather. And others said the carnage would have been greater if students had been outside or on the road when the storm hit.

Gov. Bob Riley defended administrators' actions after a tour of the school.

"I don't know of anything they didn't do," Riley said after stepping out of the collapsed hallway where the students died. "If I had been there, I hope I would have done as well as they did."

The last of the bodies were removed Friday.

The students were among 20 people killed Thursday in Alabama, Georgia and Missouri by tornadoes contained in a line of thunderstorms that stretched from Minnesota to the Gulf Coast. The storms damaged or destroyed hundreds of homes, toppled trees and knocked down power lines. In Enterprise, a town of 22,000 people, more than 50 people were hurt.

The twisters hit as a deadly winter storm walloped parts of the Plains and Midwest, keeping highways and schools closed, knocking out power and piling up huge snow drifts Friday.

At least six winter storm-related deaths have been reported in the region since the snowfall began Wednesday. Blizzard conditions shut down roads in Iowa, Nebraska and Minnesota, leaving some areas with well over a foot (30 centimeters) of snow by Friday morning.

Chicago's O'Hare International Airport had two-hour delays at midday Friday.

President George W. Bush planned to visit two of the tornado-damaged areas Saturday. The destinations were still being worked out Friday with governors in the affected states.