FOUR students have been killed and eight critically injured in a crash between a coach and a duck boat in America.

The charter coach was packed with international university students from North Seattle College when the amphibious vehicle reportedly lurched forward at a junction, clipped a car and struck the side of the passing bus in the city.

The crash forced the Aurora Bridge in Seattle to be shut as 90 firefighters helped cut passengers free from the wrecked coach.

A total of 47 patients were rushed to local hospitals for treatment.

Urgent demand for blood donors to replenish local supplies was tweeted as one hospital source said the injured were 'coming in fast and furious.'

In total, eight people were described as being in a critical condition, eight were seriously ill and one in a satisfactory condition. They include three who were undergoing surgery.

Officials said 38 other patients at other hospitals with less serious injuries.

The so-called Ride The Duck boats have been involved in previous fatal accidents, most recently in Philadelphia in 2010, when two people died.

They are used by tour operators and can drive on roads or float on water.