Minnesota Governor Tim Pawlenty said Thursday that the he Interstate 35W Bridge had been rated structurally troubled by government inspectors.

On Wednesday evening the bridge linking the twin cities of Minneapolis and St Paul collapsed over the Mississippi river, killing at least several people and injuring many others. Police said 20 to 30 people may be missing in the river and the death toll was expected to rise. According to the hospital officials, 79 people were hurt in the incident. Initially the police reported nine deaths, but later on lowered the number to four. But a final number will be announced after the rescue mission will be completed.

"We have a number of vehicles that are underneath big pieces of concrete, and we do know we have some people in those vehicles," Police Chief Tim Dolan said Thursday morning. "We know we do have more casualties at the scene."

The White House said a 2005 inspection found problems in the bridge and rated it 50 on a scale of 120 for structural stability.

"It was by no means that this bridge was not safe," said US Transportation Secretary Mary Peters, who traveled to the disaster site. "None of those ratings indicated that there was any kind of danger here."

Initially, Pawlenty said the bridge passed state inspections in 2005 and 2006 with superficial problems but no structural deficiencies.

In an official statement at the White House US President George W Bush pledged the US government's support to deal with "the terrible situation" and rebuild the bridge quickly.

"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.

Minnesota Governor Tim Pawlenty has ordered an immediate inspection of all bridges in the state with similar designs.

Built in 1967, the bridge was undergoing non-structural repaving work this summer, and some lanes of traffic appeared to have been closed at the time of the disaster, possibly reducing the number of cars and casualties. The steel-and-concrete bridge had carried more than 200,000 vehicles a day.

The National Transportation Safety Board didn’t provide any details about the repairs that were being made yesterday and Mark Rosenker, head of the government's National Transportation Safety Board, said it was too early to say what caused the disaster. It is expected that investigation

According to Rosenker, the first step of the federal investigation will the reconstruction of a part of the bridge, in an attempt to understand what happened.

The Homeland Security Department ruled out the terrorism as a possible cause. "We have no reason to think we have anything but a collapsed bridge, but we have to cover all the bases," Police Chief Tim Dolan said.