CHICAGO (CBS) — Five adults and one child were taken to the hospital Monday morning, when an extra-alarm fire swept through a three-story apartment building in the Austin neighborhood. Authorities now say the cause was arson.

Detectives from the #ChicagoPolice Arson Unit have determined the cause of the apartment fire in the 400 block of S. Laramie to be #Arson The investigation continues along with @CFDMedia and @ATF_Chicago pic.twitter.com/vDXv8krJn0 — Tom Ahern (@TomAhernCPD) July 29, 2019

The fire started around 5:30 a.m. in an apartment building at the corner of Congress and Laramie. The Fire Department called in a 2-11 alarm for the fire, bringing about 150 firefighters to the scene.

2-11 alarm EMSP 1 at 424 S Laramie will update ASAP pic.twitter.com/IAczvBHXxl — Chicago Fire Media (@CFDMedia) July 29, 2019

Deputy District Chief Anthony Ellis said, when the first firefighters arrived on the scene, heavy flames already were burning on the second and third floors in the front section of the building.

Stairwells inside the building were completely burned out as a result of the blaze, so firefighters could not reach the second and third floors from the inside, and had to rescue 10 people from the building using ladders.

“Anytime the stairwells are burned out, it provides additional challenges for us and also for the civilians trying to exit the building,” Ellis said.

Firefighters also used aerial ladder trucks to battle the flames, as the fire burned on the second and third floors and through the roof.

Two men who escaped the flames helped save a woman who was trapped in her second floor apartment, and was screaming for help.

“We woke up to someone beating on the door, telling us the house is on fire,” resident Diamond Benjamin said. “We tried to get everybody out as much as we can, but when we got out we realized that there was a lady with her legs hanging out of the window.”

Benjamin said he and another neighbor rushed over to help the woman. They couldn’t reach her, so they told her to jump from the window.

She did, and they caught her. She was taken to the hospital with a sprained ankle.

Meantime, another neighbor helped police go door to door to help neighbors get out of the burning building.

“When we actually seen the smoke, it was scary, because it’s like this is real life. You know, you can see it in the movies, and all that, but it was real life. Smoke was shooting in the hallway, and me and the officer we’re banging on the doors,” Delmario Hill said.

Ellis said a total of five adults and one child were taken to the hospital. Their conditions were not available, but officials said their injuries were not life-threatening.

The fire was extinguished by about 6:30 a.m.

Ellis said the building was not required to have a sprinkler system, but he said all residential buildings are required to have smoke detectors. He said the Fire Department was investigating whether the building had any working smoke detectors.

Approximately 20 people were left homeless because of the fire, according to Ellis. The cause of the fire was under investigation.

The building has dozens of code violations dating back to 2002, including failed inspections; and complaints about the building’s boilers, electrical work, and plumbing.