The wheelhouse and upper deck of the boat were totally gutted, but the hull was left intact and it was still floating.
The boat was not occupied last night but fishermen in a neighbouring boat were woken by the sound of the fire and alerted emergency services, Mr Swinburn said.
The fire was being treated as suspicious. Both the Greymouth CIB and the West Coast fire safety officer were today examining the scene.
"How it was started, ...it's in the early stages," Mr Swinburn said.
Putting out the fire was fairly difficult given the "hot tight spaces" below deck in gaining access for firefighters with the added fire source of fuel tanks and hydraulic fluid.
Fifteen firefighters and two appliances were at the scene for about three hours.
The brigade used a foam agent in the later stages of the incident and firefighters stayed at the scene damping down the internal structure of the boat until just before dawn.
"We also in the later stages used a pump to pump out the vessel as well."
In a statement late this morning, Greymouth police said the boat was extensively damaged.
"Police are unsure how the blaze started," the statement said.
Inquiries were under way to establish how the fire started and police asked for anyone with any information, particularly those in the vicinity of the Westfleet wharf during the early hours of the morning, to contact the Greymouth Police Station, or make contact anonymously via the 0800 CRIMESTOPPERS phone line.
- Greymouth Star