A portion of an Interstate 5 highway bridge in Mount Vernon, Wash., collapsed Thursday night, sending cars and people into the water, authorities said.
Skagit Valley Hospital in Mount Vernon, Wash., was expecting two patients taken from the accident, according to Kari Ranten, a spokeswoman. She believed a third patient was transported to another hospital. She did not know the patients' conditions.
ABC News affiliate KOMO-TV in Seattle reported rescue crews with boats were operating at the scene and rescues had taken place.
Officials were looking into reports of an oversized load "immediately" causing the collapse, said Travis Phelps of the Washington State Department of Transportation and Washington State Patrol.
The collapse occurred on the portion of Interstate 5 over the Skagit River, about two hours north of Seattle.
"N/B and S/B lanes of I-5 Skagit River Bridge collapsed," Washington State Trooper Mark Francis posted on Twitter. "People and cars in water."
The collapse occurred around 7 p.m. and the portion of the that collapsed was four lanes wide, The Associated Press reported.
Xavier Grospe, 62, who lives near the river, told the AP he could see three cars partially submerged in the water with what appeared to be one person per vehicle, with drivers on top of vehicles or sitting on open window openings.
"It doesn't look like anybody's in danger right now," Grospe said.
The bridge was built in 1955, according to The Associated Press, citing federal records.
ABC News' Ben Gittleson contributed to this report.