The blaze broke out on the second floor of the 123 Stuyvesant Ave., around 10:38 p.m., with flames extending to the attic, Deputy Kearny Fire Chief Joseph Mastandrea said.
Firefighters from Kearny, Jersey City, Kearny and Harrison had the blaze under control in a little more than an hour, Mastandrea said.
One of the occupants sustained minor injuries at the scene but refused treatment, he said.
Investigators remained at the scene Wednesday morning to determine the cause.
The 20-year-old man and his mom were staying with friends and family, respectively, friends of the family said.
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