Of the injured, three are in serious to critical condition, the Chicago Fire Department said. The “mass casualty” incident occurred at Central and West End avenues in the city’s South Austin neighborhood around 9 a.m. local time. The Chicago Fire Department responds to an explosion, Sept. 20, 2022, in this image posted on Twitter. Chicago Fire Media via Twitter “This is a confirmed explosion, but the source of the explosion is unknown,” the fire department said. Six men and two women were taken to hospitals, officials said. Their ages were not immediately clear. One of the victims was in a building across the street from the explosion, fire officials said. A building next to the blast site was evacuated, fire officials said. First responders have completed primary and secondary searches of the building with the explosion, and a final investigation is underway, Deputy Fire Commissioner Mark Furman told reporters during a lunchtime briefing. “Right now we feel like we’ve got them all out,” Ferman said. The fourth floor of the building had collapsed and was “compromised,” he said. Video from the scene shows debris strewn across pavement, roads and several cars. Windows were blown out of the building, which had extensive damage to its top floor. The Chicago Fire Department responds to an explosion, Sept. 20, 2022, in this image posted on Twitter. Chicago Fire Media via Twitter Crews from local gas company Peoples Gas did not smell any gas at the scene, a company spokesman said. “The cause of the incident is unknown, but there is no reason at this time to believe that the cause is related to natural gas or any of our equipment,” the spokesperson said in a statement. The Bureau of Alcohol, Tobacco, Firearms and Explosives and the Chicago Police Department’s Bomb Squad also responded to the investigation, the Chicago Fire Department said. The building has about 35 units, Furman said. It is currently unclear how many people have been displaced. This is a developing story. Check back for updates.