Vehicles rest on a collapsed section of the I-35W bridge in Minneapolis on Thursday morning. Emergency personnel continued searching the waters below for any bodies.

MINNEAPOLIS - Federal officials and Minnesota lawmakers prepared to travel to the Twin Cities Thursday to begin investigating the collapse of an interstate bridge into the Mississippi River. Underwater, divers searched for more bodies entombed in cars trapped beneath the twisted steel and concrete slabs of a collapsed bridge.

The Homeland Security Department said the collapse did not appear to be terrorism-related, but Hennepin County Sheriff Richard Stanek said Thursday that the cause of the collapse was still unknown.

“All indications are that it was a collapse, not an act of someone doing it,” Stanek said. He said at least a dozen submerged vehicles were visible in the water.

The official death count stood at four Thursday morning, but Police Chief Tim Dolan said as many as 30 victims were still in the water. Hospital officials counted 79 more injured.

“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 Thursday morning. “We know we do have more casualties at the scene.”

The eight-lane Interstate 35W bridge, a major Minneapolis artery, was in the midst of repairs when the bridge buckled during the evening rush hour Wednesday. Dozens of cars plummeted more than 60 feet into the Mississippi River, some falling on top one of another. A school bus hung at an angle on the concrete.

Underwater, divers were taking down license plate numbers for authorities to track down their drivers. Getting the vehicles out was expected to take days and involve moving around very large, heavy pieces of bridge.

“The bridge is still shifting,” Dolan said. “We’re dealing with the Mississippi River. We’re dealing with currents. We’re going to have to do it slowly and safely.”

‘Recovery operation’
Dolan said police estimate that 20 to 30 people were unaccounted for, though he stressed that it was just an estimate.

Fire Chief Jim Clack said Thursday that emergency work was no longer a rescue operation. “It’s a recovery operation,” he said.

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At Hennepin County Medical Center, patients had arrived in a stead stream after the collapse, some unconscious or moaning, some barely breathing, and others with serious head and back injuries, Dr. William Heegaard said.

“There was blood everywhere,” he said.

Relatives who couldn’t find their missing loved ones at hospitals gathered in a hotel ballroom Thursday for news, hoping for the best.

“I’ve never wanted to see my brother so much in my life,” said Kristi Foster, who went to an information center set up at a Holiday Inn looking for her brother Kirk. She hadn’t had contact with her brother or his girlfriend, Krystle Webb, since the previous night.

Infographic Minneapolis bridge collapse A look at the fall of the Interstate 35W bridge

Authorities initially said at least seven people had died, but Police Lt. Amelia Huffman lowered that number Thursday morning, saying, “The medical examiner’s office only has four sets of remains.” She said the initial reports were based on the best estimates authorities had Wednesday night.

As many as 50 vehicles tumbled into the river when the bridge collapsed. Many of their occupants had scrambled to shore. Some carried the injured up the riverbank, while emergency workers tended to others on the ground and some jumped into the water to look for survivors.

President Bush offered his condolences to the victims and said the federal government would help ensure that the span is 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 said Thursday in the Rose Garden following a Cabinet meeting.

First lady Laura Bush planned to travel to Minneapolis on Friday to console the victims’ families, White House press secretary Tony Snow said.

What caused the collapse?
The National Transportation Safety Board will be sending a team of investigators, NTSB spokesman Ted Lopatkiewicz said. The team will be accompanied by NTSB Chairman Mark Rosenker, Lopatkiewicz said.

Minneapolis bridge collapse news The latest on the bridge collapse ‘Cars were flying,’ survivors recall TODAY: Tales of survival, rescue Bush: Bridge will be rebuilt quickly FirstPerson: Send in your images, video | Gallery   Pictures from the collapse Recent bridge, highway collapses

Meanwhile, Transportation Secretary Mary Peters was flying to the Twin Cities early Thursday morning along with the state’s two U.S. senators, Republican Norm Coleman and Democrat Amy Klobuchar.

Peters spoke with both senators and with Gov. Tim Pawlenty, offering any help she could provide, spokesman Brian Turmail said.

While the focus has to be on emergency response, Coleman said, authorities will have to also set up a transportation system.

“Down the road, they will be doing full a forensic analysis to see what caused this,” Coleman said