INDIANAPOLIS (AP) — Splintered beams and boards on a piece of charred earth were all that remained Sunday where at least two Indianapolis homes were leveled in a blast that killed two people and rendered homes for blocks uninhabitable.

A backhoe raked through the rubble in the middle-class subdivision as clusters of firefighters and rescue workers weary from a long, chaotic day that began late the night before waited for their next assignment.

The two-story, brick-faced homes on either side of those demolished by the blast were ruins. One home's roof was gone, a blackened husk left behind. On the other side of the gap, the side of a home was sheared off. Across the street, garage doors had buckled from the heat.

It wasn't yet clear what caused the blast that shook the neighborhood at 11 p.m. Saturday. Residents described hearing a loud boom that blew out windows and collapsed ceilings. Some thought a plane had crashed or that it was an earthquake.

Alex Pflanzer, who was asleep when the nearby homes were leveled, said he heard his wife screaming and thought someone was breaking in his house. Grabbing his gun, he checked the house and saw the front door was standing open.

"I walked outside and all the houses were on fire," he said.

Pflanzer, his wife and two dogs were staying in a hotel room Sunday night. They were, however, without their cat, who refused to budge from the crawl space.

Deputy Code Enforcement Director Adam Collins said as many as 31 homes were damaged so badly that they may have to be demolished. The explosion damaged a total of 80 homes, he said. He estimated the damage at $3.6 million.

Some residents were allowed to return to their homes to retrieve a few belongings Sunday under police escort, officials said. Others whose homes weren't as badly damaged were allowed to go home, but officials said they would have to do without electricity overnight.

Officials did not identify the two people who were killed. However, a candlelight vigil was held at Greenwood's Southwest Elementary School on Sunday night for second-grade teacher Jennifer Longworth. She and her husband, John Dion Longworth, lived at a home destroyed in the blast. WTHR-TV reported that friends, family and colleagues of the teacher gathered at the school.

Deputy Fire Chief Kenny Bacon told reporters Sunday investigators haven't eliminated any possible causes for the blast. But U.S. Rep. Andre Carson, who represents the area, said he had been told a bomb or meth lab explosion had been ruled out.

Bacon said the crisis could have been much worse. "I know we're very fortunate that some of the people weren't home," he said.

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 held his ears and said, "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 what was left of the neighborhood, one home 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 had minor injuries, fire officials said.

Dan Considine, a spokesman for Citizens Energy, said the utility had not received any calls from people smelling natural gas in that area.

"Most of the time, when there's a gas leak, people smell it," he said. "But not always."

Carson said officials from the National Transportation Safety Board and the federal Department of Transportation, which have oversight over pipelines, were also sending investigators.

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. Others had to leave their animals behind, and police said later in the day that they were trying to round up those wandering through the area and find their owners.

Most evacuees eventually left the school to stay with relatives, friends or at hotels.

The relief operation was later moved to a church just a few blocks away, where residents could find supplies including blankets, shoes, diapers, canned goods and even a teddy bear.