An explosion at an East Point apartment complex Thursday was traced to an underground gas pipe line, a fire department spokeswoman said Friday.

Four units at the Lexington apartments at 3045 Washington Road were heavily damaged in the resulting fire.

One person was treated at the scene for minor injuries, and a pregnant woman caught in the apparent eruption was taken to a nearby hospital for observation.

“Our investigation is complete,” spokeswoman Renita Shelton said Friday. “The fire was caused and preceded by an explosion from an abandoned gas pipe that ran under the building.”

Tami Gerke, a spokeswoman for AGL Resources, the parent of Atlanta Gas Light, said Friday that the company was continuing its investigation into the explosion.

Resident Trevor Joiner said the occupants of his apartment woke up early Thursday morning smelling gas and reported it. Apartment maintenance workers went around turning off the gas and returned later in the afternoon to turn it back on and re-light pilot lights, he said.

About 15 minutes later, the explosion happened, Joiner said.

The explosion happened shortly before 2:30 p.m., neighbors said.

"A huge boom woke me out of my sleep," said Patrice Welch, who lives across the parking lot from the burning building. "It sounded like a bomb went off and shook the whole house."