A superyacht with a guide price of $US49.5 million ($NZ60.79 million) has been extensively damaged in a fire in the premises of award-winning boat builder McMullen & Wing in Auckland on Sunday.

McMullen & Wing managing director David Porter told NZ Newswire he had not been able to view the damage to Star Fish but he had been told it was extensive.

He said Star Fish was a newbuild due for completion early next year.

Star Fish is a 50m long steel and aluminium luxury expedition motor yacht built for Aquos Yachts, a company owned by a Hong Kong investor.

Aquos charters its existing superyacht Big Fish for $US245,000 a week.

Star Fish is longer than Big Fish to allow for a sixth stateroom and give it capacity to carry a seaplane or a submarine.

The yachts have granite decking, swim platforms and extensive storage for "toys".