SAN ANTONIO — The National Transportation Safety Board said it was sending a team Wednesday to investigate two natural gas-fueled home explosions that injured five people Tuesday evening in the 15000 block of Preston Hollow Drive in north San Antonio. The agency said it would examine why no evacuations were issued prior to the second explosion.

The first blast happened shortly before 6 p.m. Tuesday, and a second explosion was heard two doors down shortly after 8 p.m., with flames shooting into the sky from the second home. Three homes were damaged and five people, including a child, were taken to area hospitals with burn injuries.

San Antonio Fire Chief Valerie Frausto said people were inside both homes at the times of the blasts. Two adults and one child injured in the first fire were taken to the hospital with life-threatening burn injuries, according to the San Antonio Fire Department. A man and a woman tended to by medical personnel after the second explosion were also transported with life-threatening burn injuries.

A family of three injured in the first explosion — a local pastor, a high school teacher and their teen daughter — was in stable condition Wednesday. The conditions of those hurt in the second explosion were unclear.

"It was very similar to the first. The roof blew, there was sheet rock and insulation across the street," Frausto said of the second blast. A fire department spokesperson said the first home sustained extensive damage and likely will be demolished, and said the initial explosion may have been caused by a buildup of natural gas, though that determination is preliminary.

A total of 15 houses were evacuated — five houses in both directions from the two original explosions as well as across the street, according to the fire department. Frausto said gas and power had been shut off to the area. "We can't allow anybody back to their homes until it's safe," she said.

CPS Energy said in a statement it was still investigating the cause.