A freeway bridge over the Mississippi River in Minneapolis, Minnesota, collapsed Wednesday, killing at least six people and plunging cars and tons of concrete into the water below. (Xinhua Photo)

Four people were confirmed dead and at least 79 others injured when an eight-lane freeway bridge in Minneapolis, Minn., collapsed into the Mississippi River below Wednesday, according to updated casualty figures.

Minneapolis police chief Tim Dolan said 20 to 30 people are still missing.

He and other officials expected the death toll to rise as rescuers search for missing people or bodies.

"We have a number of vehicles that are underneath big pieces of concrete, and we do know we have some people in those vehicles," Dolan said.

"We know we do have more casualties at the scene," he said.

City fire chief Jim Clack said that emergency work was no longer a rescue operation and had become a recovery operation.

In Washington, U.S. President George W. Bush offered his condolences to victims of the collapse and promised that the federal government would help ensure that the bridge will be rebuilt as quickly as possible.

"We in the federal government must respond, and respond robustly, to help the people there not only recover, but to make sure that lifeline of activity -- that bridge -- gets rebuilt as quickly as possible," Bush told a press conference at the Rose Garden of the White House.

White House spokesman Tony Snow said an inspection two years ago had found structural deficiencies in the bridge, but "this doesn't mean there was a risk of failure."

He said First lady Laura Bush will visit Minneapolis on Friday.

Snow said the Minnesota state has not made a formal request for Bush to issue a disaster declaration, but people are being sent to the scene from a number of federal agencies, including the Federal Emergency Management Agency, the Environment Protection Agency and the Federal Bureau of Investigation and the National Transportation Security Board.

In addition, he said the federal government will give local officials 5 million U.S. dollars to re-route traffic and remove debris.

Meanwhile, members of the state's congressional delegation are flying home with Transportation Secretary Mary Peters.

The Interstate 35W bridge collapsed at about 6:05 p.m. local time (2305 GMT) during Wednesday's rush hour, plunging cars into the river.

Security camera video showed the bridge's center section collapsing into the river in less than four seconds. The northern end of the span appeared to drop first and the southern end followed.

At present, rescuers are continuing their search in the Mississippi River below the bridge among the submerged cars and twisted steel left by the collapse. Their hopes of finding survivors have dimmed.

Editor: Yan