The large fire broke out at a building on Broadway Avenue at East 154th Street in Harvey. The Harvey Fire Department was dispatched there at about 4:50 p.m.
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"Everybody out here that you see has pretty much lost everything today," said Willie Payne III, who lives in the building.
People who live in the building said at least one person jumped from a window to escape as flames shot from the roof.
Two people went to the hospital in critical condition, fire officials said. A Harvey police officer was injured while trying to recover a person jumping from the third floor.
"I just moved here. I just moved into that building and I lost everything," Rhonda Sims said.
The fire was under control at by 7:51 p.m., fire officials said. It is not yet clear if anyone is seriously hurt and there's no word on the cause.