SEATTLE - The Seattle fire chief says four people died at the scene of a crash involving a charter bus, an amphibious tour vehicle and two passenger cars.

Chief Harold Scoggins said at a news conference Thursday that 12 were critically injured, higher than previously reported. Many others received minor injuries.

Seattle Mayor Ed Murray says there were foreign students on the charter bus. Murray says efforts were being made to contact their consulates, but he had no other details.

Murray called the incident a "terrible tragedy."

A witness says she was walking across a Seattle bridge just after the crash happened, and came upon a mess of jumbled metal and glass.

Jahna Dyer, a registered nurse, told The Associated Press on Thursday that some victims were sprawled out on the pavement while others milled about seemingly in shock and falling down.

Another witness, John Mundell says he was at the south end of the bridge when he heard a screech and twisted metal and saw what appeared to be a few dozen people on the ground. Mundell says wanted to help the injured but "felt helpless."

Officials have not said what caused the crash Thursday.

Amphibious, military-style tour vehicles like the one involved in Thursday's wreck are operated by a tour company called Ride the Ducks and are known for exuberant drivers and tour guides who play loud music and quack through megaphones as they lead tourists around the city.

A man who answered the phone at the Ride the Ducks corporate office says the company had no immediate comment.