The fire started around 3:40 a.m. Friday on the 200 block of Woodlawn Avenue in Hamilton Township, Mercer County, at s 2 1/2 story wood-frame duplex.
The fire quickly went to a second alarm before it was brought under control, and video showed the home severely damaged.
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The baby and a woman in her 40s were found dead inside the home, the Mercer County Prosecutor's Office said.
Three others were taken to the hospital with injuries.
Officials said another house was also damaged by the flames.
There is no word on how the fire started.
The Mercer County Prosecutor's Office is leading the investigation.
Anyone with information is asked to contact Detective Anthony Sturchio at (609) 989-6406.
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