At least two people in critical condition were pulled from the house at the center of the blast and taken to Christus Spohn Memorial Hospital and later flown to San Antonio Military Medical Center's burn unit.
A third person requested treatment but refused transportation.
"The investigation is continuing," Corpus Christi Fire Chief Andy Cardiel said. "The gas department is checking their lines, their meters and their valves to see if they had any kind of release. It's going to be way too early to determine what a cause is at this point."
As a precaution, utility workers cut gas and electric service to the whole neighborhood.
Witnesses came from nearby to help pull people out of the wreckage when they heard the blast.
"The house had exploded," said Mike Obenhuas, who was eating at an IHOP a few blocks away when the explosion occurred. "We saved a little boy, a little girl, a mom and dad. Then the adjacent house started catching fire."
"There was another guy, in the initial fire, laying in the middle of it. We pulled him out. He had cuts all over his body, and he was spurting out blood," he said. "It was a pretty bad sight."
Firefighters said three houses around the blast site sustained moderate-to-heavy damage, while the home at the center was destroyed. Further away, windows were broken and doors shifted to the point where they would not close.
"At this point, we are very fortunate that the injuries are limited to three victims," Cardiel said.