An interstate bridge jammed with rush-hour traffic suddenly broke into huge sections and collapsed into the Mississippi River, pitching dozens of cars 60 feet (18 meters) into the water and killing at least six people.
Click here to see photos of Bridge collapses into Mississippi River in Minneapolis
The eight-lane Interstate 35W bridge, a major Minneapolis artery, was in the midst of being repaired and had several lanes closed when it crumbled Wednesday evening.
"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. "At this point there is nothing to suggest that this was anything other than a structural collapse."
Jamie Winegar was sitting in traffic shortly after 6 p.m. (2300 GMT) 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."
Mayor R.T. Rybak said at least six people were killed. There were no immediate reports on the total number of injured, but Dr. Joseph Clinton, emergency medical chief at Hennepin County Medical Center, said the hospital treated 28 injured people - including six who were in critical condition.
Other hospitals also were treating the injured. Clinton said at least one of the victims had drowned.
The Homeland Security Department also said the collapse did not appear to be terrorism-related.
Gov. Tim 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.
The steel-arched bridge, which was built in 1967, rises about 64 feet (nearly 20 meters) 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 had just crossed the bridge before it crumpled into pieces.
Christine Swift's 10-year-old daughter, Kaleigh, was on the bus, returning from a field trip and called her mother. "She was screaming, 'The bridge collapsed!"' Swift said.
She said a police officer told her all the kids got off the bus safely.
It appeared that the center section of the bridge dropped straight down and pancaked in the middle of the river, leaving several vehicles stranded on a broken island of wreckage. As divers plumbed the waters, other rescuers searched frantically for victims amid broken, zigzagged sections of blacktop. Some of the injured were carried up the riverbanks.
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 weren't completely in the water.
The bridge was built with a single 458-foot-long (140-meter-long) steel arch to avoid putting any piers in the water that might interfere with river navigation.
Ramon Houge told the St. Paul Pioneer Press that he was on his way home from work on the bridge when he heard a rumbling noise, saw the ground collapse and cars go down.
He said cars backed up as best they could and he parked in a construction zone and was finally able to turn around and drive off the bridge. "It didn't seem like it was real," he said.
Workers have been repairing the 40-year-old bridge's surface as part of improvements along that stretch of the interstate, the Minneapolis Star-Tribune reported on its Web site.