PORTLAND, Ore. (KOIN) — A Dollar Tree store went up in flames and led to a 2-alarm fire early Saturday morning in North Portland after its roof became “dangerously unstable,” fire officials said.

According to Portland Fire & Rescue, crews were sent to a report of a commercial fire around 2:18 a.m. at the dollar-store chain’s 7740 N Lombard Avenue location.

When they arrived, fire officials said they found the entire inside of the store was filled with smoke and half the building was on fire, including the roof. Firefighters who were sent to battle the blaze on top reported heavy flames coming through the roof, making it “dangerously unstable” and likely that the HVAC unit would fall through.

PF&R brought the firefighters back down, and officials said in a Tweet the heating and air conditioning unit did collapse through the roof.

Both levels of the store’s two-level roof caught fire and partially collapsed, PF&R said. (Courtesy/PF&R)

Officials said they called for backup and the fire was upgraded to a second-alarm. Firefighters backed off and started dousing the flames with hoses, but they ran into several complications.

PF&R said the fire ignited natural gas “which burned until crews were able to shut off the gas at the meter.” In addition, officials said the building’s lightweight roof material and large open interior contributed to the heavy flames and gasses inside.

About 10 minutes later, the fire was quelled enough for crews to reenter the building, and the blaze was extinguished soon after. Fire officials said they found no one inside, and no injuries were reported.

The cause of the fire is still under investigation.