A major freeway bridge in Minneapolis collapsed into the Mississippi River during the evening rush hour Wednesday, plunging dozens of vehicles into the water and killing at least seven people.

Hundreds of paramedics, firefighters, police divers and emergency crews converged on the scene, where tonnes of concrete were piled in the river, trapping cars and people.

A bridge across the Mississippi River in Minneapolis collapsed at 6:05 p.m. CT Wednesday.
(KMSP-TV/Associated Press)

"We're trying to work as hard as we can to pull people out of there," Kristi Rollwagen, the local deputy director of emergency preparedness, told CNN shortly after the 6:05 p.m. CT collapse.

She said an estimated 50 vehicles were believed to be underwater and she pleaded for area residents to donate blood, stay off their cellphones and stay away from the area of the collapse.

Minneapolis fire chief Jim Clack told reporters in the hours after the collapse that more than 60 people were sent to hospitals with injuries. He confirmed seven people had died, and said he expected that number would rise.

Tonnes of concrete plunged into the Mississippi River during the collapse in Minneapolis on Wednesday.
(KMSP-TV/Associated Press)

By 11 p.m. CT, the operation officially turned into a recovery mission, with Clack saying the liklihood of finding more survivors "is very slim." Divers were pulled from the water after dark because of fears they could be injured in the mounds of twisted, jagged concrete and metal lying on the river bed.

"It will be a very tragic night when it is over," Minneapolis mayor R.T. Ryback told reporters.

School bus full of children caught in collapse

In the first hours after the collapse, firefighters were trying to put out at least one fire — a tractor-trailer hanging off the collapsed bridge.

Witnesses said the truck was beside a school bus carrying about 60 children and adults, all of whom are believed to have escaped. About 10 were sent to hospital, with one adult suffering from a broken back, officials said.

Christine Swift's 10-year-old daughter, Kaleigh, was on the bus, returning from a field trip. The girl called her mother minutes after the collapse.

"She was screaming, 'The bridge collapsed,"' Swift said.

As rescue personnel worked, engineers were on the scene to monitor the bridge for signs of a secondary collapse.

'I've never seen anything like this'

Witnesses reported seeing rescue workers carrying survivors up the riverbank.

"I've never seen anything like this," said Gregory Wernick, who crossed the bridge about 10 minutes before the collapse. 

Other witnesses said the collapse sounded like a plane crash and sent clouds of dust billowing into the sky.

"It just came down, a crash, smoke everywhere," Ross MacMillan, 39, told the Minneapolis Star Tribune newspaper. "A whole bunch of people were screaming, people were trapped in their cars.''

Melissa Hughes was driving across the bridge when it collapsed. Her car fell and pickup truck landed on top of it.

"You know that free-fall feeling? I felt that twice," said Hughes, 32, who was not injured.

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

Repair work being done at time of collapse

The entire span of the Interstate 35W bridge collapsed where the freeway crosses the river near University Avenue in Minneapolis.

Surface repairs were being done to the arched bridge, which rose 20 metres above the river and was built in 1967.

Minnesota Gov. Tim Pawlenty indicated the structure was inspected in 2005 and 2006, and no major problems were identified.

"Obviously this is a catastrophe of historic proportions," Pawlenty said.

The Minnesota Department of Transportation told MSNBC and other news outlets that 200,000 cars a day cross the bridge.

At the time of the collapse, traffic on the bridge was bumper-to-bumper, with many vehicles bound for a 7:10 p.m. CT Minnesota Twins game at the nearby Metrodome, the Star Tribune reported.

The U.S. Homeland Security Department said there is no indication the collapse was caused by an act of terrorism.

With files from the Associated Press