A natural gas explosion pushed the walls of an Alpena garage off its foundation Sunday night, firefighters say.

The south side Alpena Township fire station received a call just after 4 p.m. from a North Street homeowner who reported a loud bang in his garage and a small fire on the garage ceiling.

The homeowner had been able to extinguish the fire with a garden hose.

After an investigation, firefighters attribute the explosion to a buildup of natural gas inside the garage, probably caused by a gas leak, ignited when the garage’s furnace kicked on.