About 25 firefighters attended the incident on the Tranquillity at Peterhead harbour just before 10.30pm on Thursday, with three jet hoses needed to extinguish the fire.
The RNLI’s Peterhead lifeboat took firefighters aboard their vessel to tackle the blaze and a rescue operation was launched in the harbour for potential casualties. No-one was injured.
The fire service said that one man was rescued from the harbour basin but it is understood it was unrelated to the fire.
The boat had been in port since November 4 and had been undergoing maintenance work. An investigation is being launched into the cause of the fire.
An RNLI spokesman said: “The Peterhead lifeboat was asked to launch by Aberdeen Coastguard to search for a person or persons who may have abandoned a blazing fishing boat in the harbour basin.
“There were reports that there may have been two people in the harbour. One person was recovered by the harbour pilot boat and the lifeboat then searched the harbour area for a number of hours without finding any casualty.
“It then stood by the burning fishing boat and helped to cool the deck as an aid to firemen.”