A tour vehicle and a charter bus carrying foreign students have collided in Seattle, Washington state, leaving four people dead, US officials say.
TV footage showed an amphibious "Ride the Ducks" vehicle - a type used for tours in several US cities - smashed into the side of the bus on a bridge.
The four victims were foreign students from North Seattle College. Several people were critically injured.
Seattle Mayor Ed Murray described the crash as "a terrible tragedy".
It happened at about 11:00 local time (18:00 GMT) on Thursday. Two smaller vehicles were also involved in the crash.
Most of the victims were on board the charter bus.
"Today, the North Seattle College community learned devastating news that four of our students were tragically killed in a vehicle accident on the Aurora Bridge," the school said in a statement.
"Additionally, several students remain in critical condition, and other students and a North employee sustained serious injuries."
It did not say what countries the four victims were from, adding that "government officials are working to contract next of kin".
A witness told a news station that the duck boat signalled to move left when it lurched and the front left wheel came off. It then clipped a vehicle before colliding with the bus, which was travelling in the other direction.
Forty-four people were taken to hospitals, including 12 with critical injuries, according to fire department officials.
"Ride the Ducks" vehicles, which can drive on roads and float on water, have been involved in multiple fatal accidents.
Two people died when one collided with a barge in Philadelphia, Pennsylvania, in 2010.