Thunder Bay firefighters say a man is at hospital in stable condition following an early morning house explosion.

The explosion happened in the 800 block of St. Clair Avenue around 4:20 a.m. on Thursday.

The man had first- and second-degree burns to his upper extremities, but was alert and conscious when paramedics took him to hospital.

His common-law partner said he told her he lit a cigarette and the house exploded.

Fire officials found the home in pieces when they arrived. The front door was in the middle of the street.

Fire chief John Hay said there was an explosion, but investigators have not confirmed what caused it.

Hay also said houses around the building were evacuated as a precaution, but none of the other residences sustained major damage. Most of the surrounding homes were without gas and electricity for a while Thursday morning.

Investigators were combing through debris Thursday in an effort to pinpoint a cause.

Andrea Stass is the manager of communications for Union Gas, which had employees on the scene.

"We have done an initial examination, testing the soil for gas, testing our pipeline for leaks. And our initial examination shows there's no evidence that it's related to the Union Gas pipeline system," she said.