Overnight a boat has been destroyed by fire in Manly Boat Harbour.

Fire crews were called to the scene of a boat on fire at approximately 3:45 am Sunday morning. 

The boat was ablaze for more then an hour before fire crews were able to get the upper hand.

No ocupants were on board when the fire started.

One witness said in an interview, "the inital flames comming from the boat were 30 or 40 feet high"

Fears are growing that the boat could sink if not dealt with quickly.

Fire crews do not yet know what started the blaze.