An explosion flattened a house in suburban Pittsburgh on Wednesday, killing a man, injuring his granddaughter, and damaging 14 neighboring homes, authorities said.

A utility spokesman said evidence pointed to a natural gas explosion, but the source was unclear.

Richard Leith, 64, of Trafford, died at UPMC Mercy hospital in Pittsburgh shortly after 3 p.m. said John J. Smith, an investigator with the Allegheny County Medical Examiner's Office. He was thrown into the middle of the street by the blast, Holiday Park Fire Chief Larry Glass said.

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Gianna Pettinato, 4, was found amid debris after she was "literally blown out of the house," neighbor Lynn Celia told reporters. Plum Borough Police Chief Frank Monaco said she had a broken femur but her injuries were apparently not life-threatening.

"That she wasn't killed is a miracle," he said, according to the Pittsburgh Post-Gazette. The girl was taken to Children's Hospital of Pittsburgh, where a spokesman said he did not have further details. No other injuries were reported.

Pieces of burnt insulation and debris were scattered over a 1,000-foot area, and part of the home's roof was perched precariously on a nearby tree, Glass said.

Houses on either side were heavily damaged and will have to be town down, Allegheny County Emergency Management Chief Robert Full said. Forty nearby homes were evacuated, including 12 that sustained lesser damage, he said. An emergency shelter was set up at a nearby school and authorities said they hoped residents would be able to return Thursday once utility service was restored.

Neighbor Nancy Wineland, 55, said she was cooking in her house when the explosion shook the house, cracking one of her windows. She said she ran through her house to check for possible damage before going outside, where she saw "flames and smoke and debris everywhere."

"The smoke was so thick, you couldn't see anything," she said. "You couldn't even breathe."

"All of a sudden all the pictures blew off the walls, we heard a loud bang. It felt like an earthquake," said Diane Fulmer, 43, who lives two houses away. Fulmer said she ran outside and "all I could see was parts of houses flying in the air."

Elmore Lockley, a spokesman for the Dominion Peoples natural gas utility, said evidence pointed to a natural gas explosion, but there were no problems with gas lines on that street or neighboring ones. He said investigators would look at pipes and appliances inside the house.

Lockley said there had been no reports of odors before the explosion that might indicate a gas leak and no major construction in the area in recent months. But Glass said the smell of natural gas hung in the air as firefighters arrived.

Full said the National Transportation Safety Board, which has jurisdiction over utility pipeline safety, will also investigate.