Guests staying at the Summercamp Hotel in Oak Bluffs had to be evacuated Saturday night after a malfunctioning hot water heater started a small, smoldering fire.

Firefighters were called to the Lake avenue hotel Saturday shortly before 7:30 p.m. after a report of smoke in the building, Oak Bluffs fire officials said.

Fire crews found smoke coming from a basement crawl space below a water heater in the Overlook building, a secondary part of the hotel.

Heavy smoke was coming from the fire, but it had not caught into a full blaze yet, said Oak Bluff deputy fire Chief Stephen Foster.

The hotel was open at the time and 65 people who were staying in the Overlook building had to be relocated. Guests in the main portion of the hotel were able to return Saturday evening.

The fire is still under investigation but the malfunctioning water heater is believed to be the cause.

The hotel was bringing a plumber out to work on the heater. Firefighters from Tisbury and Edgartown provided help at the scene. Mr. Foster praised his fire crews, those from other towns and the Oak Bluffs police department.

“Everyone did a phenomenal job,” he said.

If the fire had gone unabated, it could have spread further and threatened the nearby cottages.

“It could have been much worse,” Mr. Foster said. “We were very lucky.”