Smoke poured through Waldwick Pizza, as well as the adjacent Waldwick Bar and Liquors, Waldwick Wash and Dry and Giant Farmers Market on Wyckoff Avenue.
Firefighters forced open the pizzeria's rear door to get at the flames, which were tamped by sprinklers.
A second alarm brought additional manpower to the smoky blaze.
No injuries were reported.
Borough Police Officer Jake Wanamaker was on patrol when he heard the alarm, saw the fire and alerted emergency responders, Lt. Thomas Dowling said.
Authorities were investigating the cause, the lieutenant said.
"The Health Department also was notified and was conducting a follow-up investigation," Dowling said.
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