Work was being done on the house's water line when the gas line was hit and ruptured, causing the explosion, Fairborn Fire Marshal Carl Day said. It is unclear whether anyone died in the explosion.
The house was demolished, throwing debris and the victims - including an infant - into the yard. Some of the victims were airlifted to hospitals.
Crews were searching the rubble for the unaccounted person, believed to be an older man, Day said.
Neighbor Cybil Poole told the Dayton Daily News that the explosion, which occurred 100 meters from her house, felt like a car hitting it. She said she saw the infant was burned, bloodied and covered in glass.
"It was horrible. It was like a movie scene. You see this huge fireball and you see people come out of it on fire," she said. "If everybody made it out of there alive, it's truly a blessing. Obviously their lives will be changed forever."
Another neighbor, Paula Corelli, told the newspaper that she was almost hit by a flying piece of wood from the explosion. When she saw two adults running down the sidewalk carrying three bloodied children, she offered to take them while the adults returned to the scene.
"Medics told me to keep them awake because they had head injuries, so we sang to them, me and another woman," she said. "And we didn't let them look back. It was still on fire and there was a lot of blood."
Day said four juveniles were among the injured: three children, ages 1, 3 and 5, as well as a teenager. Their identities were not released, but Day said the juveniles were not believed to be the children of the injured adults.
The children were taken to Dayton Children's Medical Center, where the infant was listed in critical condition. Another child was still being examined, while two were expected to be treated and released, spokesman Terry Fink said.
Details about the adult victims, including their ages and the extent of their injuries, weren't immediately available.
The gas has been turned off to the residence after the fire was put out, Day said. He some of the neighbors who had been evacuated were allowed to return.
"Our focus right now is making the scene safe and tending to the victims," Chas Kelley, a spokeswoman for Vectren Corp., told The Associated Press from an airplane getting ready to take off for Fairborn.
Kelley said it hasn't been confirmed that there was a gas leak and the company would likely conduct its own investigation into the cause of the explosion.