The fire broke out in an apartment on the seventh floor, in the rear of the building, on South Munn Avenue in East Orange just before 9:45 p.m.
The child was run out of the building by firefighters and raced to University Hospital in Newark, where he was pronounced dead.
They were later identified as 55-year-old Willie Neal Springfield and her 3-year-old grandson, Shaquan Brown.
Both the grandmother and the grandson were residents of the 7th floor apartment on South Munn Avenue in East Orange where the fire started. The fire was isolated to the 7th floor.
Other units in the apartment sustained smoke and water damage.
Firefighters rescued dozens of other residents, carrying many of them out on their backs.
"The condition was severe. Basically, as the crews ran to knock down the fire, the victims were found in an area that was untenable for human life," East Orange Deputy Fire Chief Christopher Weiss said. "Numerous people were rescued. The entire building was loaded with smoke."
Many of those residents were treated for smoke inhalation.
Residents of the building, which has 10 stories 200 apartments, were temporarily evacuated. A nearby community center on South Munn Avenue was set up as a temporary shelter.
The cause of the fire is undetermined, but at this time it does not appear to be suspicious. East Orange and Essex County authorities are still investigating.
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