An 80-year-old man is in hospital with a fractured skull and another man has been charged after a fight broke out between two passengers on a Sydney ferry last night.

Police say two tourists got into a fight on board the Queenscliff ferry as it headed from Circular Quay to Manly about 6:00pm (AEDT).

A 31-year-old man from Tasmania allegedly hit the 80-year-old man from Cairns, in Queensland's north, who then stumbled and fell to the ground, striking his head.

The ferry had to be turned back and the older man was taken to St Vincent's Hospital while police arrested the younger man at the wharf.

He has now been charged with reckless wounding and is expected to face a Sydney court later today.

The fight happened during the evening peak hour, and caused delays while passengers were unloaded and allowed to board another ferry.

Buses had to be put on to replace the Queenslciff, which is one of three ferries that operate between Manly and Circular Quay.