FITCHBURG, Mass. (AP) — The state Fire Marshal’s office says an explosion at a Fitchburg auto parts store was caused by a natural gas leak in a pipeline, and has ruled it an accident.

The office released its finding into Tuesday’s explosion on Wednesday.

The explosion at Victory Auto Parts at about 5:20 p.m. caused extensive damage to the building, but left the owner and a customer inside at the time were unharmed.

Building Commissioner Robert Lanciani called the building a total loss. Several other buildings in the area were damaged.

Owner John Tate says there was no warning, just a ‘‘big bang.’’

He says his building does not have gas service.