GARDNER — With one wall of 167 Pleasant St. bulging and threatening to collapse onto an adjacent building, city officials Monday morning ordered the demolition of the three-story apartment building that was hit by a predawn fire.

As an excavator from Bourgeois Construction Co. moved into place to begin demolishing the building, Fire Chief Ronald Therrien said there was no choice but to tear it down after the fast-moving fire damaged all three floors.

“It’s structurally unsound,” he said.

There were no serious injuries in the blaze, reported at about 3:30 a.m.

The demolition company moved in just before noon, preparing to raze the building as fire crews finished dousing the remains of the four-alarm blaze.

The building is owned by Colonial Cooperative Bank. Mayor Mark P. Hawke said the city will pay for the demolition and seek reimbursement from the bank’s insurance company. Officials were working with urgency because, they said, the building was in danger of collapsing.

The second apartment building, at 163 Pleasant St., sustained minor damage, notably to its siding. Therrien said the tenants will probably be able to return to their apartments after the other building is demolished.

The fire started in the basement of 167 Pleasant St. and quickly spread up the walls of both buildings. The cause has not been determined. State and Gardner investigators were at the scene throughout Monday morning.

Firefighters arriving shortly after the fire was reported were able to keep the fire from getting inside 163 Pleasant St.

Jeffrey Pellom of 28 Baker St. was one of the first people on the scene. In an interview Monday morning, he said he had been sitting on his porch thinking of going to bed around 3 a.m. when a friend, Tim Dobbs, told him there was smoke coming from a nearby building. When Pellom realized the building at 167 Pleasant St. was on fire, he ran over and began yelling for people to get out. He went inside and headed to the apartment of first-floor tenant Dana Chaisson, but Chaisson was already on the third floor waking up tenants there. All six residents got out safely.

Pellom then went next door to get those tenants evacuated. By then, police had arrived and all tenants of the second building were safely evacuated, including Nicole Van Veleck, who is nine months pregnant.

“I’m glad he didn’t come today,” she said of the baby she is expecting.

Van Veleck and Anthony Messore, the baby’s father, live on the third floor of 163 Pleasant St. They said they were thankful firefighters were able to save their apartment, which is on the same side as the destroyed building.

Therrien said firefighters initially went into 167 Pleasant St. with hopes of controlling the fire there. When it proved too far out of control, the firefighters focused on saving the building next door.

The chief said their effort saved the second building.