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DENVER (KDVR) — A fire sparked at an apartment complex, leaving three people hurt and many more without a home. The flames sparked on Monday evening at South Federal Boulevard and Exposition Avenue.

A black charred building, shattered windows and debris were left behind at the Boulevard Gardens apartments after a fire ripped through. According to the Denver Fire Department, someone knocked on the station door around 6 p.m. to alert firefighters of the flames. Firefighters rushed to the complex and were met with aggressive flames and smoke.

Crews were able to put out the flames in 20 minutes, with 65 firefighters battling the blaze that left behind significant damage. No official cause of the fire has been determined, but Denver Fire said it sparked on the first floor and flames spread up to the second and third floors.

The aggressive flames and smoke made it difficult for residents to get out. Firefighters performed a heroic rescue, using a ladder to rescue three people trapped on the second floor.

“We had two firefighters put up a ladder behind, said Capt. Greg Pixley with Denver Fire. “They assisted these individuals right above the fire. It was a dangerous situation, but we were aggressive in our ability to get them away from the fire and smoke.”

Three people were taken to the hospital, but their injuries were not considered critical.

On Monday night, families with young children were seen wrapped in blankets trying to get warm. Besides the fire damage, there is also heavy water and smoke damage in several units. The American Red Cross is helping impacted families get back on their feet.

An extensive investigation is underway to determine how the fire sparked.