The blaze broke out inside the LongHorn Steakhouse on 50 International Drive South just after 12 a.m. Tuesday.
Firefighters from the Flanders Fire Department, Budd Lake Fire Department and surrounding mutual-aid companies battled the flames all night.
Video from NewsCopter 7 just before dawn showed the restaurant was completely destroyed.
Three firefighters were injured. All are expected to be okay.
The fire appears to have been gas-fed.
The cause will be investigated by the Morris County Prosecutors Office.
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