The Ottawa police arson unit investigated a west-end overnight house fire that left three people homeless, their fourth investigation in four days.

Arkell Street house fire

This house on Arkell Street was heavily damaged by fire leaving three people homeless. (CBC)

Ottawa firefighters responded to 976 Arkell St. in the Frank Ryan neighbourhood just after 1 a.m. Thursday, near the intersection of Carling Avenue and Richmond Road.

A 911 call had reported flames shooting from the house and a vehicle. Firefighters attacked the blaze from outside the home.

"We heard a loud bang, sounded almost like an explosion," said neighbour Chris Kazen. 

"A second explosion happened, (which) shook the window of the house. We opened up the curtains to find the neighbour's car and his carport up in flames."

The main body of the fire was knocked down just after 2 a.m.

Nobody was injured, but three adults were left homeless because there was so much damage to the home.

Investigators deemed the fire suspicious and the police arson unit came to investigate, saying late Thursday afternoon they're leaning toward it being accidental.

"We called in the investigation team because we were concerned about how quickly it spread," said Sgt. Dave Christie of the arson unit, adding they still want to get a second opinion.

Fire officials say there is an estimated $450,000 of damage and the home "will not be habitable."