Five people have been taken to hospital after a ferry crashed into a pier at Circular Quay, leaving 18 people injured, one seriously.

Multiple ambulances were called to the scene after the crash, which happened at around 4.15pm on Tuesday.

It is understood the supercat smashed into a wooden backboard on one of the piers at Circular Quay after it got into trouble reversing.

A NSW Ambulance spokesman said 18 people were assessed by paramedics after they fell during the crash.