The fire broke out on the top floors of a building at 343 Grove Street between Bay and Morgan just before 2:00 p.m.
An Italian restaurant, Buon Appetito, is located on the ground floor. Apartments are located above it. Some 22 people have been displaced by the fire.
The flames also spread to a building at 345 Grove Street, but fire chief Darren Rivers says some 90 firefighters are working to keep the flames from spreading beyond those buildings.
Four firefighters have suffered minor injuries. They were taken to Jersey City Medical Center.
Plumes of heavy smoke filled the air for hours. Port Authority says some smoke even reached the Grove Street PATH train station, but it dissipated. It is having no effect on PATH train service. The fire is about a block from the station.
Rivers says they have no indication what sparked the fire, but an investigation will begin once the the flames are out.