MINNEAPOLIS (AP) -- Rescuers have given up hope of finding any more survivors after an eight-lane bridge spanning the Mississippi River collapsed in rush-hour traffic, although more vehicles can be seen in the murky water, a rescue official said Thursday.

"At this point it is a recovery effort," said Hennepin County Sheriff Rich Stanek, speaking early Thursday after rescue attempts were abandoned for the night because of the dangers of the operation. "It's dark, it's not safe with the currents in the water and the concrete," he said.

About 50 cars were still in the water, the officials added. The collapse did not appear to be terrorism-related. The bridge linked the twin cities of Minneapolis and Saint Paul.

Minneapolis Fire Chief Jim Clack also said there were unlikely to be any survivors. "We think there are several more vehicles in the river we can't see yet," Clack said.

About 20 families had gathered at an information center, looking for information on loved ones apparently missing.

"I've never wanted to see my brother so much in my life," said Kristi Foster, who went to the center looking for Kirk. She hadn't had contact with her brother or his girlfriend since the previous night, and his cell phone was switched off.

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

The eight-lane Interstate 35W bridge, a major Minneapolis artery, was being repaired and two lanes in each direction were closed when the bridge buckled Wednesday evening, breaking into huge sections and collapsing into the river, pitching dozens of cars 60 feet (18 meters) into the water and killing at least seven.

Search lights on the banks illuminated a horrific scene of twisted wreckage, thick concrete slabs, twisted steel and crushed cars tossed about haphazardly. A line of ambulances idled along the adjacent bridge.

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

Pawlenty said the 40-year-old bridge was inspected by the Minnesota Department of Transportation in 2005 and 2006 and that no immediate structural problems were noted. "There were some minor things that needed attention," he said.

Federal officials and Minnesota lawmakers will travel to the Twin Cities Thursday to begin investigating the collapse.

The National Transportation Safety Board will be sending a team of investigators, NTSB spokesman Ted Lopatkiewicz said.

Road crews were working on the bridge's joints, guardrails and lights this week, with lane closures overnight on Tuesday and Wednesday.

Aerial shots from local television stations showed the entire span of Interstate 35W had crumpled into the river below. Some injured people were carried up the riverbank, while emergency workers tended to others on the ground and some jumped into the water to look for survivors. Fire and black smoke rose from the wreckage.

A school bus had just crossed the midsection of the bridge before it collapsed. The bus did not go into the water, and broadcast reports indicated the children on the bus exited out the back door.

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

"She was screaming, 'The bridge collapsed,"' Swift said. All 60 kids got off the bus safely, but about 10 of the children were injured, officials said.

The collapsed bridge stood just blocks from the heart of Minneapolis, near tourist attractions like the new Guthrie Theater and the Stone Arch Bridge. As the steamy night progressed, massive crowds gathered.

The river's depth at the bridge was not immediately available, but the U.S. Army Corps of Engineers maintains a channel depth of at least 9 feet (three meters) in the Upper Mississippi from Minneapolis southward to allow for barge and other river traffic.

There were 18 construction workers on the bridge at the time of the collapse, said Tom Sloan, head of the bridge division for Progressive Contractors Inc., in St. Michael. One of the workers was unaccounted for.

Sloan said his crew was placing concrete finish on the bridge for what he called a routine resurfacing project. "It was the final item on this phase of the project. Suddenly the bridge gave way," he said.

Sloan said his workers described a horrific scene. "They said they basically rode the bridge down to the water. They were sliding into cars and cars were sliding into them," he said.

Several hundred people climbed to the top of the hill in nearby Gold Medal Park, which offered a partially blocked view of the collapsed bridge. A few cried, while others stood in circles and prayed.

The steel-arched bridge, which was built in 1967, rose about 64 feet (20 meters) above the river and stretched about 1,900 (580 meters) feet across the water. The bridge was built with a single steel arch to avoid putting any piers in the water that might interfere with river navigation.

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