An early-morning fire that caused extensive damage to the interior of a vacant commercial building just outside Waikiki was intentionally set, fire investigators said.

The fire department has referred the case over to the Honolulu Police Department.

Fire Capt. Terry Seelig said firefighters were dispatched to the single-story building at 1713 Kalakaua Avenue at 3:30 a.m.

The fire was reported under control at 3:43 a.m. and extinguished by 4:15 a.m.

Seelig said no one was in the building.

Seelig said about 35 firefighters from seven companies battled the blaze.

Damage was estimated at about $60,000.