Fire crews spent hours Tuesday morning extinguishing a massive three-alarm fire at a residential building in Rockville, Md.

The fire started around 4:15 a.m. at Building G at the Gables Upper Rock Apartments on Upper Rock Circle. Montgomery County fire officials say the three-acre complex was 90 percent complete and expected to be finished in two to three weeks before this fire ripped through 150 units.

The view from Chopper4 showed the complex engulfed in flames, with the majority of the building gutted as crews fought to get the flames under control.

The apartment complex is a total loss, an estimated $15-$20 million.

"The building's been deemed unsafe to occupy, which means the stability of the walls and the roof are just not safe," said Pete Piringer of Montgomery County Fire and Rescue.

By Tuesday afternoon, crews were still at the scene, throwing water on hot spots. More than 12 hours later, it was still smoldering in spots.

"The fire was huge. The orange glow was shining into my window and woke me up. After a while, I had to leave the apartment because the smoke was coming in," said Jessica Ainsworth, who lives in a neighboring building.

Fire officials believe gas tanks inside the building were possibly feeding the flames.

There are no reported injuries.

About 200 firefighters battled the blaze.

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