Wildlife experts are monitoring a young whale hit by a Manly ferry in Sydney Harbour this morning.

They say the injury does not appear to be life-threatening but would be painful, and they want to make sure the whale is not distressed.

Harbour City Ferries reported damage to a propeller blade after confirming that the 8:40am service 'hit something'.

Passengers were dropped off and the ferry is being assessed by engineers at Balmain base.

The whales were spotted playing just inside the Harbour from the 7News helicopter.