San Antonio — Five people were injured when explosions occurred several hours apart at two homes on the same block of a north San Antonio neighborhood Tuesday night, authorities said.

The National Transportation Safety Board described the home explosions as "natural gas‑fueled" in a statement posted to social media. The NTSB, which said it was sending a team to the scene Wednesday, will investigate why no evacuations were issued prior to the second explosion. 

San Antonio Fire Chief Valerie Frausto told reporters the first home explosion occurred at about 6 p.m. local time, and the second about two hours later, around 8 p.m. People were inside both homes at the times of the blasts, she said. 

"It was very similar to the first, you know," Frausto said of the second explosion, which occurred two doors down from the first. "The roof blew, there was sheet rock and insulation across the street."

Frausto said five people, including a child, were rushed to area hospitals with burn injuries from both blasts. 

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

Neighbors told CBS News they didn't smell gas after the first blast, and there was no sign that they might still be in danger. They even said they were out in the street talking with firefighters, along with the residents of the second home that exploded. 

But according to neighbor John Young, the residents of that second home returned to it before it exploded. 

"Those people had been outside with us, watching what was going on, and they went back inside the house and…then their house went up," Young said. "I mean, it went in flames."

Frausto, asked if firefighters had made a mistake in their response to the first blast, responded, "We don't know when these things happen, when there's a gas leak, very hard to detect, and especially under these conditions, there's sometimes no odor. It's just something that happened, and we have to deal with it."

Gas and power have since been shut off to the area, and several surrounding homes evacuated, Frausto noted.

"We can't allow anybody back to their homes until it's safe," the fire chief said.

CPS Energy, the natural gas provider for the area, told CBS News in a statement that it is still investigating the cause.