The fire broke out around 12:45 a.m. Thursday, and firefighters found flames and heavy smoke when they arrived on scene a short time later.
Witnesses say the grandfather was calling out for his 8-year-old grandson. Firefighters soon got the elderly man off the porch roof and found the boy from inside the building.
The child and four adults all suffered smoke inhalation and were taken to hospitals. The child was listed in serious condition, while the adults were all in stable condition. Their names have not been released.
The cause of the fire remains under investigation.
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