CHICAGO (WGN) — Multiple people were hospitalized after a building explosion in Chicago on Tuesday morning.

First responders were on the scene at a three-story, 36-unit apartment building just before 9:30 a.m. in the South Austin neighborhood after a portion of the top floor collapsed. At least 10 ambulances were at the location.

The Chicago Fire Department said eight people were transported to the hospital. Officials said three people were in serious to critical condition. One person who was hospitalized was at the building across the street. Many residents were displaced.

“Our first concern is the health, well-being and safety of our residents,” Roman Viere, owner of the building, said in a statement. “We are doing everything we can to cooperate with emergency services, and we are ready to do whatever we can to support our residents.”

The building next door was evacuated, according to fire officials.

A woman who was near the building when the explosion happened said she thought it was a bomb that went off.

Several people who lived in the building said they were home when the explosion happened. They said the explosion rocked the entire building.

“I was asleep, and all of a sudden, there was a loud booming,” said resident Lawrence Lewis. “I woke up to my windows gone, my front door blown open. I just saw smoke, and I ran out of the house. I was asleep. I’m shook up right now.”

Some people who left not long before the explosion said they smelled something in the hallway. 

People’s Gas said there is no reason to believe this was a gas explosion. The fire department reportedly told them there was no odor of gas or equipment issues.

Mayor Lori Lightfoot issued the following statement:

“I am closely monitoring the events and both the Chicago Fire Department and the Department of Buildings are onsite at the collapse. We will provide updates as the situation develops. 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.”

The incident is under investigation. No further information was provided.