Updated

Two firefighters lost their lives Saturday while battling a blaze at the former Deutsche Bank skyscraper in downtown Manhattan, abandoned after the Sept. 11 terrorist attacks.

Officers at the scene said the building was in danger of collapse after a seven-alarm fire ripped through the vacant structure near Ground Zero, police told the Associated Press.

The blaze began about a dozen floors up in the tower.

One firefighter suffered cardiac arrest and another smoke inhalation. A third suffered minor injuries to an ankle, fire officials at the scene said.

The fire was burning on multiple floors at the building. Construction crews had already dismantled 14 of the building's 40 stories -- reaching the 26th floor on Tuesday. Some firefighters used stairs to reach the burning upper floors.

More than two hours after the blaze was first reported, the blaze was declared a six-alarm fire. Officials continued to push onlookers further back from the building and set up a command post on the West Side Highway. Officials could be seen poring over a map of the area.

The cause of the fire was unknown. Smoke pouring from the burning building was visible from midtown Manhattan and the New Jersey side of the Hudson River.

The acrid smell of smoke, which hung over the neighborhood for days after Sept. 11, returned to lower Manhattan along with the wail of emergency vehicles. More than three dozen fire vehicles, with more than 160 firefighters, responded to the blaze as pieces of burning debris fell from the building to the streets.

Scaffolding on the sides of the building was aflame as police shut down streets in the area around Ground Zero.

The building at 130 Liberty St. has become a constant headache for redevelopers in the nearly six years since the attacks. The 1.4 million square foot office tower stood as a downtown Manhattan eyesore, contaminated with toxic dust and debris after the World Trade Center's south tower collapsed into it.

Efforts to dismantle the skyscraper were halted by a labor dispute last year, along with the ongoing search for the remains of attack victims.

More than 700 bones and fragments were discovered in the contaminated skyscraper from mid-2005 to June of this year, including some positively matched this year to a previously unidentified victim. The last bones found at the building were in March, leading city officials to conclude their search three months later.

Officials did not immediately comment on whether the smoke at the scene contained any toxic chemicals. A spokesman for the Empire State Development Corp. said the agency, which is overseeing redevelopment at Ground Zero, was working with emergency officials to assess the impact of the fire.

The Associated Press contributed to this report.