Denver Fire investigators looking into a blast that leveled multi-family housing south of downtown believe exploding gas was the cause, the department spokesman said Friday morning.

One injured person was hospitalized with what firefighters said appeared to be relatively minor injuries. The firefighters have found a missing dog, Denver Fire Department spokesman John Chism said. It was dead.

Fire dispatchers received two calls about the explosion at a four-plex in the 400 block of South Lincoln Street at 6:06 p.m. Thursday evening. Firefighters raced to the scene. Typically, these are caused by blown transformers.

“It was just rubble. There was no active fire when we got there,” Chism said.

The firefighters, suspecting gas, pulled out multiple hoses as a precaution and supervisors contacted Xcel Energy officials, who shut down electricity and gas lines in the area.

Fire investigators on Friday morning hadn’t yet determined whether anybody in the area was working on a stove, furnace, hot water heater, or other gas appliance. Nor had they found evidence of construction work in the area, Chism said.

Residents in adjacent, attached buildings escaped through the ruins.

“Definitely crazy – and lucky, too,” he said.

Eight adjacent housing units, largely wrecked, have been evacuated. City building inspectors were assessing the potential for further structural collapse. Red Cross teams offered aid to the displaced residents.

After the blast, a man who’d been sitting in an adjacent second-story room climbed out and away over the rubble. And people several blocks away reported hearing the blast, Chism said. Hours later, residents nearby said they were having trouble coaxing pets who hid under furniture to come out.