Gloucester, MA – An initial investigation has discovered a leak in an underground gas pipe in front of a house that exploded here this morning, a National Grid spokesman said at a press conference late this afternoon.

However, John Higgins, a National Grid spokesman, declined to directly link the leak as the cause of the explosion, which critically injured a 30-year veteran of the city’s police department who resided in the Eastern Avenue home. The pipe with the leak was underneath the street, directly in front of the house.

“There was a gas leak, and we moved to make a repair,” said Higgins, at the City Hall press conference. “It is now complete.”

The state fire marshall’s office and state police are now heading the investigation, while local agencies will be assisting.

While officials stressed the area is safe, National Grid crews will work throughout the night, scanning the area for any other potential leaks. Officials also announced the creation of a new hotline to report gas leaks: 800-231-5325.

The explosion occurred shortly before 8 a.m. at 76 Eastern Ave., near Route 128. Officer Wayne Sargent, 59, had just finished his shift and returned home, said Gloucester Fire Chief Barry McKay. He heard some noises from the oil furnace in the basement and decided to check it out. As Sargent walked down the stair case, while calling the oil company on his cellphone, the house exploded.

Sargent, who was conscious after the explosion, was flown by helicopter to Massachusetts General Hospital. In his short time there, his condition has been downgraded from “serious” to “critical.”

The explosion damaged two neighboring houses, blowing out the windows to one house, and leaving the side of the other house substantially charred.

Earlier in the day, a National Grid spokesman more directly tied natural gas to the cause of the explosion.

“It appears that natural gas was the cause, but how it entered the house and how it may have ignited is under investigation,” said David Graves, a spokesman for National Grid.

David Swift, who lives in the neighborhood, was buying coffee at Jeff’s Variety, which is a few buildings away from the explosion, when he heard the blast. He said it sounded like a truck hit the building. He and four or five people ran over to the house and sifted through the debris to help the victim.

Sargent was standing in the basement of the house, he said.

“The house just disappeared from the street,” Swift said. “I didn’t think anybody would come out of that house after hearing that blast.”

A sales clerk, Gayle Silva, said the explosion shook the store so much that tomato paste cans, cigarette packages, and other items fell off the shelves. She said she saw the house explode through a store window, as she was waiting on customers.

“It went up so fast. There were red flames everywhere,” Silva said. “I’ve never seen anything like that before in my life.”

Chief said the department had received a few calls in the last few weeks about the smell of gas in the neighborhood. Neighbors said natural gas crews had been working on the street in the last few weeks.

Graves said this morning that he did not have access yet to work crew records for that area so he could not confirm if work had been done in recent days.

Sargent was among eight officers commended earlier this month by the department after they safely apprehended a man who locked himself in his apartment and threw butcher knives at two officers, according to a story in the Gloucester Daily Times.

Sargent is a 1969 Gloucester High School graduate.

On Dec. 17, a house explosion in Scituate killed a man who was inside. The cause remains unclear.

The state fire marshal’s office investigated but has not released any details. Police have said “human involvement” was a factor.