Authorities are searched for a temporary way to restore access after a key bridge linking the US and Canada collapsed, dumping a handful of vehicles and people into the icy water.
The three people who fell into the Skagit River in north-western Washington state escaped with only minor injuries.
The four-lane Interstate 5 bridge collapsed about halfway between Seattle and Vancouver, British Columbia, after an oversize truck hit the span, the Washington State Patrol chief said. Officials are trying to find out whether the spectacular collapse of a bridge on one of the West's most important roadways was a fluke - or a sign of a bigger problem with thousands of bridges across the US
Authorities focused first on trying to find a temporary span for the Skagit, although it will not come in time for the tens of thousands who would usually travel between Canada and Seattle during one of the busiest holidays in the US, Memorial Day weekend.
"You cannot overstate the importance of this corridor to Washington state," Governor Jay Inslee said. Traffic on the I-5 and surrounding roads was backed up for miles, a situation the governor said would continue indefinitely.
Officials were looking for a temporary, pre-fabricated bridge to replace the 50-metre section that failed, Mr Inslee said. If one is found, it could be in place in weeks. If not, it could be months before a replacement can be built, the governor said.
Trucker William Scott was hauling a load of drilling equipment when his load bumped against the steel framework over the bridge. He looked in his rearview mirror and watched in horror as the span collapsed into the water behind him.
"He looked in the mirrors and it just dropped out of sight," Cynthia Scott, the trucker's wife, said from the couple's home in Canada. "I spoke to him seconds after it happened. He was just horrified."
The truck driver works for Mullen Trucking in Alberta, the Washington State Patrol said. The tractor-trailer was hauling the equipment southbound when the top right front corner of the load struck several of the bridge's trusses, the patrol said.
The truck made it off the bridge, but two other vehicles went into the water about 25 feet below as the structure crumbled. Dan Sligh and his wife were in their pick-up heading to a camping trip when he said the bridge before them disappeared in a "big puff of dust". He added from his hospital bed: "I hit the brakes and we went off."