Four dead after tour and charter buses collide in Seattle

At least four people are dead and a further 12 critical after two buses collided in the US city of Seattle. 

Emergency services were called the Aurora 99 bridge at 11.05 am (4.05am AEST) after a charter bus carrying college students and an amphibious "duck boat" vehicle collided.

The Seattle Fire Department has confirmed at least four people have died, while around 50 more are being treated for injuries. Twelve of those are in critical conditions.

Horrific US television images from the scene show wreckage strewn across the bridge. 

Firefighters pulled injured victims from both buses and a makeshift triage centre was established on the bridge, which has been closed to all other traffic.

“We’ve had a terrible tragedy,” Seattle mayor Ed Murray told reporters at a press conference.

“There’s been a terrible loss of life.

“The thoughts of this city go out to everyone.”

It is believed all four killed were aboard the charter bus, which was carrying students and staff from North Seattle College.

The amphibious bus was a "Ride the Ducks" vehicle.

The company operates tours of Seattle, with its vehicles equipped for land and water travel.