Video: Bridge linking Washington and Canada collapses

Three taken to hospital after cars and people are dumped into the Skagit River

A major bridge linking Seattle, in Washington State, US, and Canada collapsed last night, dropping cars and people into the river below.

Authorities have said no one was killed, but three people were rescued and taken to hospital.

The four-lane motorway bridge, which is over 50 years old, crosses the Skagit River near Mt Vernon on the Interstate 5, about halfway between Seattle and Vancouver.

The cause of the collapse, which came at the beginning of one of the US's busiest holiday weekends, is still unknown. The state transportation department said it was investigating whether an oversized lorry load may have struck the bridge.

Dan Sligh and his wife were in their pickup truck heading to a camping trip when the bridge before them disappeared in a "big puff of dust."

"I hit the brakes and we went off," Sligh told reporters from a hospital, adding he "saw the water approaching ... you hold on as tight as you can."

Sligh, his wife and another man in a different vehicle were dumped into the chilly waters of the Skagit River.

"We don't think anyone else went into the water," said Marcus Deyerin, a spokesman for the Northwest Washington Incident Management Team. "At this point we're optimistic."

State patrol detectives and the patrol's commercial vehicle enforcement bureau troopers were last night talking to a lorry driver whose rig was believed to have hit the bridge.

"It appears the commercial vehicle made contact with the bridge," Washington state trooper Mark Francis said. "Whether it was the cause" of the collapse or made contact as the bridge was falling "that will all come out in the wash. But it appears it hit the bridge."

Marcus Deyerin, a spokesman of the Northwest Washington Incident Management Team, said it appeared that two vehicles — a car and the pickup truck with the travel trailer attached — fell into the river. He said the water depth was about 15 feet (nearly 5 meters), and the vehicles half-visible in the water likely were resting on portions of the collapsed bridge.

The bridge was not classified as structurally deficient, but a Federal Highway Administration database listed it as being "functionally obsolete" — a category meaning that the design is outdated, such as having narrow shoulders and low clearance underneath.

The bridge was built in 1955 and has a sufficiency rating of 57.4 out of 100, according to federal records. That is well below the statewide average rating of 80, according to an Associated Press analysis of federal data, but 759 bridges in the state have a lower sufficiency score.