The construction site of the new Marathon Oil headquarters in Memorial partially collapsed early Monday afternoon, killing three construction workers and injuring one, according to the Houston Fire Department.

All 240 construction workers are believed to be accounted for after the building’s stairwell collapsed. The identities of the victims are not yet known. According to HFD, the injured worker has been transported to a hospital in a stable condition. The fire department’s rescue team worked with an onsite engineer to ensure there were no more victims in the wreckage.

While the building itself is not in danger of collapsing, inspectors are concerned about a secondary collapse in the stairwell.

Marathon released a statement later in the day, saying:

"We are saddened to learn that an accident occurred at the construction site for the future Houston headquarters of Marathon Oil.

We extend our deepest sympathies to the families of those contractors who were affected and thank the first responders. We have offered our assistance to the building contractors as they respond to this accident."

KPRC 2 spoke to a worker at the scene who said he was on the ground floor when the collapse happened. He said it appeared that several floors of a stairwell may have collapsed.

“Out of nowhere, I hear a loud banging sound,” the worker said. “It sounded like a building was collapsing, which, I checked out, it didn’t happen, but all I saw was the parking building ... we’re very close to the parking building. All you see is a bunch of smoke.”

The high-rise building at 990 Town and Country Boulevard is set to become the new headquarters of the Houston-based oil and gas company in late 2021, when their current lease in the Galleria area expires.

In 2019, real estate information firm CoStar wrote that the project was being developed by Hines. The new tower near the CityCentre shopping district is planned to be 15 stories and 440,000 square feet.