MINNEAPOLIS – An interstate bridge suddenly broke into huge sections and collapsed into the Mississippi River during bumper-to-bumper traffic Wednesday, killing at least seven people and pitching dozens of vehicles, tons of concrete and twisted metal into the water and onto the land below.

Minneapolis Fire Chief Jim Clack said more than least 60 people were injured, and the death toll could rise after the collapse of the eight-lane Interstate 35W bridge, a major Minneapolis artery.

“It’s obviously a catastrophe of historic proportions for Minnesota,” said Gov. Tim Pawlenty.

The bridge was in the midst of being repaired and had several lanes closed when it crumbled. The cause of the collapse was unknown, authorities said Wednesday night.

Dr. Joseph Clinton, emergency medical chief at Hennepin County Medical Center, said his hospital treated 28 injured people – including six who were in critical condition.

Clinton said at least one of the victims had drowned.

According to the State Patrol, 20 people were missing. Between 50 and 60 vehicles were on the bridge when it went down, the patrol said.

Rescue efforts continued in 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 semitrailer, were on fire. People were also reportedly floundering in the river. Rescuers rushed to help people escape cars trapped in the V where the bridge had caved in.

The crumpled wreckage of the bridge lay on the east bank of the river, and a huge section of concrete roadway lay on the west bank. Down below in the river gorge, rescue workers scrambled to help people on the roadway that now lay in the gorge. Fire and black smoke rose from the wreckage.

Jamie Winegar of Houston said she was sitting in traffic 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.”

Homeland Security Secretary Michael Chertoff issued a statement Wednesday night saying there was no indication of terrorism.

The Minneapolis Twins decided to play Wednesday night’s game, but only after the public address announcer alerted the crowd at 7:08 p.m. of the bridge’s collapse. A moment of prayer followed. It was then announced that the game would go on so emergency crews could perform their duties without the added pressure of having 20,000 to 25,000 people scrambling in swarms from the Dome area.

However, the Twins postponed this afternoon’s game against Kansas City. This evening’s groundbreaking ceremony for the Twins’ new ballpark also was postponed.

The arched bridge, which was built in 1967, rose about 64 feet above the river. An estimated 50 vehicles plunged into the water and onto the land below, the Star-Tribune reported.

A burning truck and a school bus clung to one slanted slab. The bus, filled with 60 children, ages 5 to 17, was returning from a day camp and had just crossed the bridge before it crumpled into pieces, At least two children and two adults were injured, according to one of the children on the bus.

Christine Swift’s 10-year-old daughter, Kaleigh, was on the bus, returning from a field trip to Bunker Hills in suburban Blaine. She said her daughter called her about 6:10 p.m.

“She was screaming, ‘The bridge collapsed,”‘ Swift said.

Dozens of vehicles were scattered and stacked on top of each other amid the rubble. Some people were stranded on parts of the bridge that aren’t completely in the water.

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

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.

Melissa Hughes, 32, of Minneapolis said she was driving home across the bridge when she went down when the western edge in the collapse.

“You know that free-fall feeling? I felt that twice,” said Hughes, who was not injured.

A pickup ended up on top of her car, partially crushing the top and back end.

“I had no idea there was a vehicle on my car,” she said. “It’s really very surreal.”

Peter Siddons, a senior vice president at Wells Fargo Home Mortgage, was heading north over the bridge toward his home in White Bear Lake, Minn., when he heard “crunching.”

“I saw this rolling of the bridge,” he said. “It kept collapsing, down, down, down until it got to me.”

Siddons’ car dropped with the bridge, and the nose of his car rolled into the car in front of him and stopped. He got out of his car, jumped over the crevice between the highway lanes and crawled up the steeply tilted section of bridge to land, where he jumped to the ground.

“I thought I was dead,” he said. “Honestly, I honestly did. I thought it was over.”

The Associated Press and the Star-Tribune of Minneapolis contributed to this report.