A fast-burning fire swept through half of a large duplex home early Thursday before firefighters could get inside to attempt a rescue, killing five members of a family, including four children, authorities said.
The cause of the fire was not immediately known. Officials said it was the deadliest on record for South Plainfield, about 30 miles southwest of New York City.
Relatives said the fifth victim was the children's grandmother, though authorities said they were still working to identify the dead.
Authorities said four other family members were also injured, though only one of them remained hospitalized by midday.
Neighbor Isabel Scavino said her husband woke up about 3:15 a.m. to the sound of a screaming child. She said they heard what sounded like either gunshots or firecrackers as the fire tore through the house, a converted 19th century farmhouse.
Scavino said she saw a woman running from the home with a small child in her arms, and other children also fleeing.
"The fire just spread out, it was just crazy. It looked like it started on the first floor and then just spread up to the roof in about a minute," she said.
The fire was largely confined to the half of the home that was destroyed.
Fire Chief Thomas Scalera said the first floor was engulfed in flames by the time firefighters arrived, making it difficult for them to quickly get access to the second story, where all the victims were found.
Ladders were quickly put up at the back and sides of the home to try to reach the top stories, but Scalera said the flames were too intense for firefighters to get inside to try to rescue anyone.
"They are very somber right now at the firehouse," he said.
Middlesex County Prosecutor Bruce Kaplan said police and the prosecutor's office were investigating the cause of the fire.
Two volunteer firefighters received minor injuries when they were involved in a two-vehicle crash en route to the fire, Kaplan said.