MINNEAPOLIS, Mn. (AP) -- An interstate bridge jammed with rush-hour traffic suddenly broke into huge sections and collapsed into the Mississippi River Wednesday, pitching dozens of cars 60 feet into the water and killing at least seven people.

The eight-lane Interstate 35W bridge, a major Minneapolis artery, was in the midst of being repaired and two lanes in each direction were closed when the bridge buckled.

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

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."

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

Rescuers called off the search as nightfall made it too dangerous to search the waters, which were filled with chucks of the mangled bridge and at least 50 vehicles in the water.

"We think there are several more vehicles in the river we can't see yet," Clack said, adding that the likelihood of finding survivors was slim.

Authorities referred family members searching for missing loved ones to a nearby hotel, where the Red Cross had set up operations.

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.

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

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.

Police Chief Tim Dolan said officers were checking other bridges as a precaution.