The major link between the US and Canadian sides of the Pacific Northwest region was severed after a bridge collapsed, dumping a handful of vehicles and people into a river, police said. All three people who were on the span were rescued and taken to hospitals.

The four-lane Interstate 5 bridge – more than half a century old – collapsed about halfway between Seattle and Vancouver, British Columbia. Washington State Patrol Chief John Batiste blamed it on a big truck carrying a tall load that hit an upper part of the span.

The truck made it off the bridge and the driver remained at the scene and cooperated with investigators.

The accident was reminiscent of the August 2007 collapse of an I-35W bridge in Minneapolis that killed 13 people and injured another 145 when it buckled and fell into the Mississippi River during rush-hour.

The collapse came before sunset on a clear day at the start of one of the busiest holiday weekends of the year in the US, Memorial Day weekend.

Dan Sligh and his wife were in their pickup truck on Interstate 5 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,” Mr Sligh told reporters from a hospital, adding he “saw the water approaching... you hold on as tight as you can.”

Mr Sligh, his wife and another man in a different vehicle were dumped into the chilly waters of the Skagit River. They were injured, but authorities said it appeared nobody was killed in the bridge failure that raised the question about the safety of ageing spans.

The three had non-life-threatening injuries.

Mr Sligh said his shoulder was dislocated in the drop into the water, and he found himself “belly deep in water in the truck.”

He said he popped his shoulder back in and called out to his wife, who he described as being in shock initially as they waited for rescuers to arrive in boats.

Traffic along the heavily travelled route could be affected for some time.

Jeremiah Thomas, a volunteer firefighter, said he was driving nearby when he glimpsed something out of the corner of his eye and turned to look.

“The bridge just went down, it crashed through the water,” he said. “It was really surreal.”

The bridge was about eight metres above the water. Officials said it appeared that two vehicles – a car and the pickup with the travel trailer attached – fell into the river. The water depth was about 4.5 metres, and the vehicles half-visible in the water likely were resting on portions of the collapsed bridge.

Crowds of people lined the river to watch the scene unfold.

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 had a sufficiency rating of 47 out of 100 at its November 2012 inspection, Transportation Department spokesman Noel Brady said yesterday. Washington state was given a C in the American Society of Civil Engineers’ 2013 infrastructure report card and a C- when it came to the state’s bridges.

The group said more than a quarter of Washington’s 7,840 bridges were considered structurally deficient or functionally obsolete.