MINNEAPOLIS — With a shudder and a thundering crack, an eight-lane bridge over the Mississippi River in Minneapolis collapsed during rush hour yesterday, plunging dozens of cars into the murky water below and killing at least seven people.

The steel-and-concrete span of Interstate 35 buckled and swayed, creaked and then, in a terrifying instant, crumbled as though it was stepped on. Green girders and huge chunks of concrete crashed more than 60 feet into the water. One portion of the interstate caved into a jagged V, trapping several cars and drivers.

Jamie Winegar of Houston was sitting in traffic shortly after 6 p.m. when all of a sudden she started hearing "boom, boom, boom and we were just dropping, dropping, dropping, dropping."

The car she was riding in landed on top of a smaller car but did not fall into the water. She said her nephew yelled, " 'It's an earthquake!' and then we realized the bridge was collapsing."

The bridge, a major Minneapolis artery, was in the midst of being repaired and had several lanes closed when it crumbled.

"There were two lanes of traffic, bumper to bumper, at the point of the collapse. Those cars did go into the river," Minneapolis Police Lt. Amelia Huffman said. "At this point, there is nothing to suggest that this was anything other than a structural collapse."

Minneapolis Fire Chief Jim Clack reported seven deaths from the bridge collapse. Several dozen were injured, including six critically, said Dr. Joseph Clinton, emergency room chief at Hennepin County Medical Center.

Clack said 60 people were taken to area hospitals for treatment and that the death toll could rise.

"This is a catastrophe of historic proportions for Minnesota," Gov. Tim Pawlenty said.

By 1 a.m. last night, Hennepin County Sheriff Rich Stanek said all search efforts had been called off for the night and that searchers did not expect to find any survivors.

"It's dark, it's not safe with the currents in the water and the concrete and rebar," he said. "At this point it is a recovery effort."

About 20 families gathered at an information center, looking for information on loved ones they couldn't locate.

The Homeland Security Department said the collapse did not appear to be related to terrorism. The National Transportation Safety Board planned to send a team of investigators to Minneapolis today, NTSB spokesman Ted Lopatkiewicz said.

All but one of the construction workers who were working on the bridge at the time were accounted for, said Minneapolis Police Chief Tim Dolan.

INSPECTED LAST YEAR

The steel-arched bridge, which was built in 1967, rises about 64 feet above the river. It was built with a single 458 foot-long steel arch to avoid putting any piers in the water, which might interfere with river navigation.

Pawlenty said the bridge was inspected by the Minnesota Department of Transportation in 2005 and 2006 and that no structural problems were noted. "There were some minor things that needed attention," he said.

Rescue efforts continued into the night as people spilled into the streets and watched from vantage points in and near downtown Minneapolis.

What they saw was the aftermath of a horrific scene that unfolded as motorists crawled bumper to bumper across I-35 toward the end of rush hour.

They felt buckling and swaying and heard a crunching.

Then came the unthinkable: The 40-year-old bridge collapsed, dumping an estimated 50 vehicles into the water and onto land below. That was followed by scenes of frantic, bloodied motorists and rescuers who converged on the scene.

Many vehicles, including at least one semi-trailer, were on fire. People were reported to be floundering in the river. Rescuers rushed to help people escape cars trapped in the V-shaped hollow where the bridge had caved in.

A school bus, filled with 60 children, ages 5 to 17, returning from a day camp was on the bridge when it collapsed, injuring at least two children and two adults seriously, according to one of the children.

"We collapsed," said Ryan Watkins, one of the children.

He said the bus bounced twice and then stopped. He and others escaped out the rear door of the bus because the front door was wedged against a concrete traffic barrier. The kids were returning from a day of swimming.

"Some kids had blood on their faces, but thank God, everybody could move," said Jay Danz, 45, of St. Paul, who had just driven under the bridge. "Everybody seemed OK."

Catherine Yankelevich, 29, was on the bridge when, she said, "it started shaking, cars started flying and I was falling and saw the water."

Her car was in the river when she climbed out the driver's side window and swam to shore uninjured.

"It seemed like a movie, it was pretty scary," said Yankelevich, who is from California and survived the 1994 Northridge earthquake.

"I never expected anything like this to happen here," she said.

Memorial Blood Centers and the American Red Cross put out immediate calls for blood donors.

A LIFE SAVED

Marcelo Cruz, 26, of Crystal, Minn., who has used a wheelchair since being paralyzed in a shooting in South Carolina several years ago, was driving his van across the bridge toward downtown when he felt it began to wave up and down. He steered into the concrete railing to stop himself from driving into the river, and saw many cars on the bridge fall into the water.

His van came to rest steeply inclined toward the river and several onlookers ran and told him to get out. He said he needed help and the onlookers carried him out of his van in his wheelchair to safety on the riverbank.

"I'm lucky to be alive," he said over and over again.

The Minneapolis Star Tribune, Los Angeles Times and Associated Press contributed to this report.