INDIANAPOLIS >> Officials say as many as 31 homes were damaged so badly in a blast that killed two people in Indianapolis that they may have to be demolished.

Deputy Code Enforcement Director Adam Collins estimated the damage at $3.6 million.

Deputy Fire Chief Kenny Bacon told reporters Sunday investigators haven’t ruled out any possible causes of the late-night blast that was heard miles away.

But a congressman who represents the Indianapolis neighborhood says investigators have ruled out a bomb or a meth lab.

U.S. Rep. Andre Carson said he had received that report from Homeland Security officials during a tour of the devastated middle-class subdivision.

Residents described a loud boom that shook their homes, blew out windows and collapsed ceilings.

Aerial photographs of the once-tidy neighborhood of one- and two-story homes showed at least two had been reduced to blackened pits of debris. Other homes had sections gutted by fire or holes in their roofs or exterior walls. Siding dangled from the outside of other homes, and crumpled garage doors hung from houses nearby. Pieces of wood and other building materials littered the street and surrounding properties.

It wasn’t clear what caused the blast about 11 p.m. Saturday. Firefighters responding to a call about a single house fire were surprised by a much bigger blaze. The fire centered on four homes, two that were leveled and two others that only had the frames standing by the time the flames were extinguished, Deputy Chief Kenny Bacon said.

The damage extended two blocks in every direction, he said, and fire officials didn’t initially realize the extent of it in the darkness. Mark Lotter, a spokesman for the mayor, said later Sunday that 27 homes were uninhabitable, and eight had significant damage.

Residents described a loud boom that shook their homes, blew out windows and collapsed ceilings. They rushed outside to find a chaotic scene with flames rising against the Indianapolis skyline to the north.

Bryan and Trina McClellan were at home with their 23-year-old son Eric when the shock wave from the blast a block away shook their home. It knocked out the windows along one side of their house, and their first instinct was to check on their grandchildren, two toddlers who were in the basement. One was holding his ears and saying “Loud noise, loud noise.”

Eric McClellan said he ran to the scene of the explosion and saw homes flat or nearly so.

“Somebody was trapped inside one of the houses, and the firefighters were trying to get to him. I don’t know if he survived,” he said, adding that firefighters ordered him to leave the area.

Once the flames were out, firefighters went through the rubble and damaged homes one at a time in case people had been left behind, Fire Lt. Bonnie Hensley said. They used search lights until dawn as they peered into the ruined buildings.

Along with the two people killed, seven people were taken to a hospital with injuries, Bacon said. Everyone else was accounted for, he said.

Four of the seven who were injured minor injuries, fire officials said. They did not provide details on the others or identify those killed.

An investigation was underway, said Bacon, who would not rule a gas leak in or out.

Dan Considine, a spokesman for Citizens Energy, said people usually smell gas when there is a leak, but the utility had not received any calls from people smelling gas in that area.

Dan Able, a 58-year-old state employee who lives across the street from the two homes that exploded, said his first thought was that a plane had hit his house.

The blast was “a sound I’ve never heard before, it was so loud,” he said. His windows blew out and a bedroom ceiling collapsed on his wife, Jan. He pulled her out, and they went outside.

“Both houses across the street were on fire, basically, just rubble on fire,” he said.

The Ables and about 200 other people evacuated from the neighborhood were taken to a nearby school. Some who had been sleeping arrived in their pajamas with pets they scooped up as they fled. Most eventually left to stay with relatives, friends or at hotels, but seven or eight remained through the night, sleeping on cots.

Some came back Sunday to pick up supplies from tables covered with baby food, wipes, blankets, and other essentials.

Among those awakened by the blast was Pam Brainerd, a 59-year-old hospice nurse.

“I was sleeping on the sofa and all of a sudden, my upstairs windows were blowing out and my front door was falling in,” Brainerd said. “My front door came off the frame. It was the largest bang I’ve ever heard.”

She stepped outside and saw what she described tall flames one street away. “There was a house engulfed in flames, and I could see it spreading to other houses,” she added.