Chicago fire official responded to a structure collapse in South Austin Tuesday morning. 

The collapse, caused by a reported explosion, left several injured. The CFD tweeted that five ambulances had been requested to Washington Street and Central Avenue. The number was later increased to 12. 

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Chicago fire officials said that three of the injured were in serious-to-critical conditions.

The explosion at the three-story, 36-unit apartment building in the South Austin neighborhood occurred shortly before 9:30 a.m., officials said. 

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“Requesting manpower for searches in structure,” the department tweeted.

Photographs and video posted on the Chicago Fire Department’s Twitter page shows that much of the top floor of the four-story brick apartment building on the city’s West Side was destroyed by the blast. Scores of bricks and other debris had fallen onto the street, crushing at least one car and seriously damaging two others.

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

“I was asleep, and all of a sudden there was a loud booming,” Lawrence Lewis, who was asleep at the time, told WGN television. “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.”

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No cause of the explosion had been determined. The department said in a series of tweets that the Chicago police bomb squad and agents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were on their way as well.