The three-alarm fire started at around 4 a.m. in a single-family home near the corner of Madison Avenue and South 15th Street. Flames also spread to a house next door.
"Right now, we're investigating how the fire started," Anthony Ambrose, of the Essex County prosecutor's office, told The Star-Ledger. Officials don't suspect foul play.
Though authorities have yet to release the names of the dead, it's believed that at least several were related.
He described them as "a very sweet family. ... They all loved the Lord."