The fire broke out just before 3:30 a.m. in the 2800-block of South Keeler Avenue, and spread to the home next-door, CFD said.
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One adult victim was taken to Saint Anthony Hospital in critical condition.
Several people have been displaced, and a CTA warming bus is on the scene.
RELATED: 2 injured in Austin house fire, CFD says
It was not immediately clear later Tuesday morning how the fire started.
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Emergency crews remained on the scene about 6 a.m.
This is a developing story; check back with ABC7 Chicago for updates.