Investigators probe Sydney ferry smash

Crash investigators are questioning a ferry crew to determine how and why their vessel ploughed into Sydney's Circular Quay.

Eighteen people were injured and five hospitalised after the SuperCat, en route from Watson's Bay, slammed into the wharf on Tuesday afternoon.

All injured passengers have since been released from hospital.

Up to 100 passengers, mainly tourists, were on board the ferry when it crashed.

It's remains unclear whether human error or engine issues caused the crash.

An independent probe - spearheaded by the Office of Transport Safety Investigations - is examining all aspects of the smash, including weather conditions, vessel maintenance and manoeuvring of the vessel.