Investigators from the state Fire Marshal’s Office have determined that a fire Wednesday night in a vacant building in Old Orchard Beach was arson.

Sgt. Joel Davis said the fire at 29 Old Orchard St. started around 10:15 p.m. in a second-floor apartment. The fire caused extensive damage to that apartment and to an apartment on the third floor. A seasonal business on the first floor, which sells T-shirts and beachwear, was not damaged.

Davis said Old Orchard Beach firefighters did a good job containing the fire, which easily could have spread to several surrounding wooden buildings that are vacant because they’re used for seasonal businesses.

The owner of the building lives in New York state.