It was vacant, and the gas service had been turned off, company spokesman David Spigelmyer said.
The second collapsed home was owned by a man who had been living at a nursing home, said Ray Wappes, 47, the longtime owner of a rental house across the street that was damaged.
The American Red Cross was helping 10 adults from seven families with services including food, clothing and shelter, the charity said in a statement. Equitable Gas Co. was paying for their lodging for the night, Red Cross spokesman Brian Knavish said.
The utility shut off natural gas service to the area, north of downtown.
Authorities received a report of a collapsed house around 10:30 a.m. and discovered the two homes destroyed, Pittsburgh Public Safety Director Michael Huss said. Authorities later said at least 24 other houses were damaged.
Huss said he could not confirm that an explosion had flattened the houses because an investigation was still under way. Police and emergency workers were combing the neighborhood to account for residents, he said.
Shortly after the blast, dozens of people gathered nearby to gaze at a huge pile of rubble where the houses once stood. Bricks had landed on the roof of a neighboring house, and windows shattered as far away as two blocks. Shards of glass were scattered on sidewalks and streets, and workers cleared debris as a light rain fell.
Darrin Adkins said he called 911 after he drove past the house and felt an explosion. Later, a telephone pole in front of the houses leaned precariously over the road.
"I'm just glad I wasn't right beside it," said Adkins, 40. "It snapped that pole like a twig."