CFD tweeted just after 9:20 a.m. that five ambulances had been requested to Washington Street and Central Avenue. The number was later increased to 10.
[Ads /]
Chicago fire officials said at least eight people were injured in the incident, three of whom were serious-to-critical. One of those injured was from a building across the street.
RELATED: Roof collapses after fire breaks out at Fuller Park home; no injuries reported, CFD says
The blast that tore through the top floor of the building could be felt blocks away.
South Austin building partially collapses: CFD
"My foundation of my home shook like an earthquake," said Ashunda Harris, who lives in an apartment a few blocks away. "I saw a cloud of smoke from the building. It was a foundation type of smoke, not like smoke from a fire."
Eric Hune was knocked clean off his feet.
"I just got up off the floor. I didn't even see myself fall down. I got up off the floor and just ran straight out the door," he said. "I woke up off the ground. I don't remember hitting the ground. I just remember getting up and running."
The third floor hallway, he said, was a fog of chaos, a mix of disorienting panic, dust and doors blown off hinges.
"As I was running out they couldn't see where to go, there was so much smoke, so they just followed behind me," he said. "So many of us running out, I couldn't count."
CFD spokesman Larry Merrit said they believed everyone was accounted for by about 10:30 a.m.
Fire officials said the explosion took place on the upper floor of the apartment building, but it is not yet known what caused it. It was so powerful, it shattered windows, covering cars in the street with bricks and glass. Nearby buildings were also evacuated and schools were dismissed early.
South Austin explosion injures 8 residents, neighbors before building collapse
Chicago fire officials said two male victims were taken to Loyola University Medical Center; one was in critical condition and the other remained stable.
Another male victim and a female victim were taken to Mount Sinai hospital. They also remained stable.
Another female victim was taken to West Suburban Medical Center where her condition is stable, and another male victim was taken to Mount Sinai Hospital where he is in critical condition, Chicago fire officials said.
[Ads /]
A male victim whose condition is stable and male victim in critical condition were also taken to Stroger Hospital.
Victims suffered burn injuries and traumatic injuries, fire officials said.
Several of the victims have since been released to the hospital, somehow with few visible injuries.
"I just got an ache to my shoulder and a bad migraine," Hune said.
At this point it's not known how many people were displaced, but the Red Cross is providing food and shelter at Circle Urban Ministries down the street.
"I got all kinds of medication, and they told me to take this to Walgreens in the morning and Red Cross will pay for all my medication," said Betty Pugh, displaced resident.
"What's next? I have no idea. I'm just glad to be alive right now at this point," said her son Lawrence Lewis.
The explosion was so powerful, people in other buildings suffered injuries and needed treatment.
"It knocked me literally off the chair to the wall to the floor," said Tavares Hamilton who lives across the street with his brother. "I've got injuries to my arm. I have ringing in my ear, my leg from the impact of the explosion and hitting the wall."
WATCH: CFD responds to South Austin building collapse
CFD: 6 hospitalized after South Austin explosion, building collapse
"A large burn on the body can be months and months of treatment, not to mention the recovery after that," said Dr. Joshua Carson, Loyola University Medical Center burn center medical director. "So it really can be anything."
Carson said burns to the body can sometimes also complicate how other traumas are treated.
"These building collapses, explosions, is that the burns are overwhelming, and everybody sees the burn when the patient comes in, and what you really have to do is to make sure your team knows not to get distracted and not forget about the other kind of trauma they can't see," he said.
Online inspection records for the building that exploded reviewed by the I-Team reveal a history of inspection failures and alleged code violations.
The I-Team received clarification on some of this from officials at the Chicago Department of Buildings. Authorities say "none of the violations (in city records) would have contributed to an explosion or structural failure at the building."
READ MORE: Chicago building that exploded has history of inspection failures, alleged code violations
Roman Viere, the owner of the building, said in a statement, "This is a devastating event and we are heartbroken for all of our residents.
"Our first concern is the health, well-being and safety of our residents. We are doing everything we can to cooperate with emergency services, and we are ready to do whatever we can to support our residents."
WATCH: 'It's very tragic': West Side alderman reacts to building collapse
[Ads /]
'It's very tragic': West Side alderman reacts to building collapse
Peoples Gas crews were responding to the scene.
A spokesman for the company said there was no reason to believe the cause is related to gas or any of their equipment.
WATCH: CFD deputy commissioner describes response to building collapse
CFD deputy commissioner describes response to building collapse
The Bureau of Alcohol, Tobacco, Firearms and Explosives is on the scene, as is the CPD bomb unit.
In a statement, Mayor Lori Lightfoot said, "My thoughts are with those who were injured and displaced in the building collapse in the Austin neighborhood. We must also thank the brave men and women of the Chicago Fire Department who are working to abate the dangerous conditions. I am closely monitoring the events and both the Chicago Fire Department (CFD) and the Department of Buildings (DOB) are onsite at the collapse. We will provide updates as the situation develops."
ABC News contributed to this report.