UPDATE: The Colorado Springs Fire Department has ruled the Sunday night fire at the Retreat at Austin Bluffs to be accidental, caused by careless smoking.
Smoking materials were disposed of in a potted plant on a third-floor patio, The plant ignited, then caught materials next to it on fire.
The fire then spread to a 20-pound propane tank attached to a barbecue grill.
A three-alarm fire that displaced 20 residents and scorched 12 units at the Retreat at Austin Bluffs apartment complex Sunday night burned into Monday morning, as Colorado Springs firefighters continued to battle it.
The fire department's Twitter feed showed a new alarm called firefighters back to the apartment complex at 8:43 a.m., as hot spots in the building sparked back to life.
"The building is not safe right now, so the firefighters are having to put out the hot spots from the outside, on a ladder," fire department spokeswoman Sunny Smaldino said. "The Heavy Rescue Unit is on scene and they will evaluate the building's structural safety before investigators go in."
Investigators worked through the night to interview all of the building's tenants, none of whom were harmed by the blaze, Smaldino said.
The Red Cross and the apartment building's administrators helped the displaced residents find temporary housing, provided them with necessary emergency items and even helped start insurance claims, Smaldino said.
At about 10:13 p.m. Sunday, some residents of the complex at 4615 Hinsdale Way called police with reports of an explosion or possible shots fired.
The third floor of the apartment building was engulfed in flames when officers arrived, prompting the evacuation of two adjacent buildings until 1:15 a.m., police said.
The extent of the damage to the building, or whether its occupants will be allowed to return, is unknown.
Stay with gazette.com as we follow this story.