A BRIDGE carrying a freeway over a river in the northwestern US state of Washington has partially collapsed, sending cars and people plunging into the water below, police say.
At least three people were fished out, but there were no reports of serious injuries or fatalities in the incident, which may have been caused by a high-sided truck hitting a bridge span, a spokesman said on Thursday.
Pictures showed a large, mangled section of the bridge, which carries the Interstate 5 highway over the Skagit river north of Seattle, collapsed into the water, with traffic and crowds of people visible on the end nearest land.
“People and cars in water,” Mark Francis, spokesman for the Washington state highway patrol, said on his Twitter feed.
The police did not immediately return calls seeking more details, including on potential casualties.
The four-lane road bridge, built in 1955 according to reports, is some 95km north of Seattle.
The I-5 freeway runs up the US West Coast, north from the scene of the collapse to the Canadian border towards Vancouver.
At least two cars were in the water, and three people were rescued from vehicles, Marcus Deyerin, spokesman for the Northwest Washington Incident Management Team, told the Seattle Times.
Rescuers believed they had pulled everyone involved out of the water, but they were not sure, he added, saying the section of bridge collapsed about 7pm (1200 AEST Friday).
A law enforcement source cited by the Seattle Times said about 140 metres of freeway collapsed, sending a car, a truck and a trailer into the water some 40 metres below.
“It’s a hell of a ride,” the source was quoted as saying.
Reports suggested the collapse may have been triggered by a large truck hitting some part of the bridge structure.
“We are looking at a potential over-height load,” Travis Phelps, a spokesman for the Washington State Department of Transportation, told Kiro 7 television.
Witness Dale Ogden told KING 5 television he saw the truck strike the bridge.
“I was less than 50 feet (15 metres) away from the truck when it hit it … I had just passed it in the fast lane southbound and it had an oversized load.
“It was approximately 12 feet (3.6 metres) wide and over 14 feet (4.3 metres) tall … I saw the truck strike the right corner of the bridge. It almost tipped the truck over, but it came back down,” he said.
“It tipped it up to about a 30-degree angle to the left and it came back down on its wheels and almost instantaneously behind that I saw girders falling in my rear view mirror.”