At least eight people were taken to the hospital after an explosion caused a residential building to partially collapse in Chicago on Tuesday morning, fire officials said.
Three of the injured were in serious to critical condition, Chicago Fire Department Director Larry Langford tweeted.
One of those transported to the hospital was across the street at the time of the explosion, Marc Ferman, the deputy fire commissioner, told reporters.
The cause of the explosion was not immediately known.
“No one knows what the heck caused it,” Langford told the Chicago Sun-Times.
A bomb squad was called in to assist, as were agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives.
The blast occurred at approximately 9 a.m. on the city's West Side, with bricks and debris from the building covering the street below.
The building had approximately 35 units, but it's unclear how many people were at home at the time of the explosion, Ferman said. An adjacent building was evacuated as a precaution.
Engineers used struts to secure the structure so emergency crews could search the upper floors for additional victims.
"We're confident we got everybody out," Ferman said.