Updated

Superstar swimmer Michael Phelps and his Club Wolverine teammates were headed for an afternoon practice for the U.S. Olympic trials when the tornado sirens sounded.

"Really ominous, that's for sure," recalled two-time Olympian Erik Vendt, Phelps' roommate during the meet.

Severe storms swept through the Plains on Friday, forcing the swimmers in Omaha to flee pools and run for cover. Strong winds in neighboring Iowa killed two teenagers and knocked out power to thousands.

Officials at the Qwest Center near downtown Omaha closed the building to examine it after Phelps and hundreds of other athletes were herded into hallways because of a tornado warning.

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Water poured into the building, down arena steps and onto the deck of the competition pool during the storm. The storm's winds may have reached 100 mph in some areas, said meteorologist Bryon Miller.

Repairs were under way at the Qwest Center and practices were to resume Saturday, according to USA Swimming spokeswoman Jamie Olsen.

An eight-day meet to decide the U.S. Olympic swimming team opens Sunday.

Across the Missouri River in Council Bluffs, Iowa, two 18-year-old men died when a tree fell on the car they were in while they were at a friend's house, said Police Sgt. Jason Bailey. Authorities used a backhoe to free a 15-year-old girl trapped in the back seat.

Damage reports in the region included toppled trees and power lines and hail the size of baseballs. Flash flood watches were issued across Iowa, where flooding has been a problem recently.

In Detroit, about 1 1/2 inches of rain were dumped on the downtown area during the evening rush hour. Freeways and some surface streets were made impassable.

No serious injuries were immediately reported in Omaha, but there were reports of a few house fires caused by lightning, said Al Berndt, assistant director of the Nebraska Emergency Management Agency.

Hundreds of people had gathered for a 6 p.m. outdoor concert and for an arts festival in downtown Omaha. Booths flipped over, and awnings and other covers were whipped away by strong winds.

The outdoor concert and fireworks were canceled.

A spokesman for the Omaha Public Power District said more than a third of its customers were without power. The district serves 330,000 customers. There were widespread power failures in Council Bluffs, and Bailey said the police department was on auxiliary power.

The Missouri River Wastewater Treatment Plant, which serves the Omaha area, lost power and untreated wastewater was being discharged into the Missouri River, said Joe Gudenrath, spokesman for Omaha Mayor Mike Fahey. City officials told people to avoid wading or swimming in the water in the stretch of the river that passes by Omaha, and several miles downstream.

Outside the Qwest Center, chunks of what appeared to be material from the building were scattered about.

After the storm had passed, the Qwest Center was cleared and swimmers headed outside to snap pictures of sheet metal and other material that had been blown around.