UNION, Maine — A fire and explosion of still undetermined origins destroyed an unoccupied home here early Thursday morning.

The force of the 3 a.m. explosion broke windows and cracked walls in a home about 100 feet away, according to Sgt. Joel Davis of the Maine Fire Marshal’s Office. Union Town Manager Jay Feyler said the explosion woke him up at his North Union home located about a mile away.

First responders initially were not sure whether anyone was in the building at the time, but the homeowners eventually were located at about 8 a.m. at a hotel, said Davis.

The house, which was built circa 1900 and is owned by Dal Riley, was undergoing major renovations, according to Assessor James Murphy.

The fire was reported shortly after 3 a.m. on Sunk Haze Lane off Common Road. Chandler Farley, who lives in a nearby apartment above the Common House of Pizza, said the explosion rocked the building he lives in. He said he looked outside and did not see anything at first but then saw a flicker like a campfire between some trees down the road.

His son, Kyle Farley, said he ran down to the scene and the house was engulfed in flames and debris was scattered around the yard. Windows in a neighboring home had been blown out by the explosion, he said.

The elder Farley said a couple lived in the old farmhouse and that the man who lived there was renovating to rent out part of it.

Fire investigator Davis said late Thursday morning that propane tanks were located next to the home, but that the cause of the fire and explosion had yet to be determined. Assistant Fire Chief Jesse Thompson said the house was being heated by portable propane heaters.

Firefighters from Union, Appleton, Hope, Rockport, Washington, Warren and Waldoboro battled the blaze.

An excavator was called in at about 5 a.m. to help move debris.

The Knox County Sheriff’s Office had Common Road blocked off at the Union Commons. The road was closed until about 10 a.m. while it was cleared of debris.