STRONG – A three-story multi-unit apartment building was extensively damaged Sunday after a fire broke out in a storage room at the 34 Church Hill residence.

When firefighters arrived, it was totally engulfed in flames.

No one was home when the fire was reported at 8:30 a.m., state fire investigator Chris Stanford said Monday.

The cause of the fire is undetermined, Stanford said, due to extensive damage in a first-floor bedroom that was used as a storage room where the fire originated.

The owner of the building, Mona Knowles, had left with her companion, Mark Stottlemyer to go to Massachusetts to visit his son, fire Chief Scott Dyar said.

The couple left about 7:15 that morning, Stanford said.

The other two apartments were vacant, he said.

About 50 firefighters from Strong, Farmington, New Vineyard, Kingfield and Phillips turned out to fight the blaze, Dyar said.

NorthStar Emergency Medical Services personnel and Phillips and Strong fire department auxiliaries responded, he said. Five trucks were used, including Farmington’s new aerial-pumper.

The structure was not burned to the ground, Stanford said, but there is major structural damage and some areas of the roof burned off.

“Nobody was injured,” Dyar said.

The American Red Cross was contacted and several residents and a Beal’s General Store representative offered places to stay as well as clothing.