Maribella died at Hackensack University Medical Center just before noon and her grandmother, Margaret, at St. Barnabas Medical Center in Livingston shortly after, Police Chief Ralph Verdi told Daily Voice.
The girl "was the last one taken out," he said. "They were doing CPR on her at the scene."
Maribella's grandmother was carried out by firefighters and hospitalized with severe burns, the chief said.
Witnesses said an explosion ignited the fire, which injured 10 people in all.
Three police officers were checked out at a local hospital and released -- one with a twisted knee and the others with smoke inhalation -- after they rushed in to rescue residents.
"We don't have any breathing apparatus," Verdi said. "They just went in and did what they had to do."
Police Lt. Chris Boel was on routine patrol when he heard an explosion and saw fire around 11:30 a.m. He arrived to the sounds of screams as people tried to escape the three-story multi-family home on Washington Avenue, the chief said.
Boel summoned help and rushed into the building, with Officers Dominick Verdi and Angelo Ratto soon close behind.
A neighbor who lives across the street said she'd just gotten home, got out of her car and was putting the key in her door when she heard an explosion.
She ran to a local fire station and activated the pull-box alarm.
The Bergen County Prosecutor's Arson Investigations Unit remained at the scene Wednesday morning. The county sheriff's Bureau of Criminal Identification collected evidence.
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