A fire that started early Sunday morning has damaged an Oak Bluffs restaurant that was planning to open this spring.

At 3:48 a.m., Oak Bluffs fire crews responded to 6 Circuit avenue after a report of smoke detectors going off, said deputy fire chief Stephen Foster. When firefighters arrived they found smoke coming from the basement of the building.

The location is the former space occupied by The Cardboard Box, where Mikado is planning to open its second Island restaurant and the building has been undergoing renovations.

Firefighters were on fire watch at the former Cardboard Box location Sunday. — Ray Ewing

A sprinkler in the building largely contained the fire, which, according to fire chief Nelson Wirtz, was caused by the careless disposal of smoking materials, Mr. Foster said.

Firefighters found a box with rags in the building and believe the fire started there before spreading to a wooden table.

Fire crews from Tisbury and Edgartown aided Oak Bluffs at the fire, Mr. Foster said. The building, which had about a foot and a half of water in it, was then ventilated. Residents who live above the restaurant were able to return to their apartments.

“We were lucky to have the fire mainly knocked down,” Mr. Foster said. “The sprinkler system did exactly what it was supposed to do.”

Firefighters were staying on Circuit avenue throughout Sunday to monitor the building.

Mikado got approvals from the town in January to open the Oak Bluffs restaurant. The unit was formerly home to the Cardboard Box.

Proprietor Xi Yu had previously said he planned to open the new location on April 1. A request for comment to the business was not immediately returned Sunday.