NORCROSS, Maine — A fire that smoldered for hours destroyed an unoccupied camp building on an island in North Twin Lake on Thursday, officials said.

Firefighters from Medway, Millinocket and the Maine Forest Service shuttled themselves and their equipment by two boats to what Millinocket Assistant Fire Chief Thomas Malcolm identified as Tate Island, where a passerby reported the fire at about 2:55 p.m. Forest service workers returned to the island on Friday morning to douse a flare-up in the building’s remains, Malcolm said.

Owned by Scott Joslyn of York, the one-story wood building was destroyed by the time Millinocket firefighters arrived with an engine, rescue boat and ambulance, Malcolm said. Firefighters arriving from Medway found “fire everywhere” when they arrived, Medway Fire Chief Jon Buckingham said.

“The camp was gone, there was an out building starting to go, and the tops of the trees were all ablaze,” said Buckingham, whose department responded to the fire with five volunteers.

A passerby contributed another boat to the effort. Firefighters doused the flames at 5:45 p.m. on Thursday.

Malcolm said the fire’s cause will be logged as undetermined. The building’s electrical service was disconnected. Neighbors, however, reported lightning strikes on Wednesday night.

“I wouldn’t be surprised if the lightning strike happened at night probably around 2:30 a.m. or so. It might have smoldered for awhile before it just flared up and went,” Malcolm said.