About 60 firefighters battled the blaze, which broke out about 4 a.m. at the Brothers Diner One in the 100 block of Trenton Road in Browns Mills, said Browns Mills Fire Chief Andre McClain.
"The building is completely gutted," McClain said. "When we arrived, it was already under heavy fire conditions and extended throughout the building."
Fire crews worked for about two hours and kept the blaze from spreading to a convenience store about 15 feet away, McClain said.
When the fire broke out, the restaurant was closed and no one was inside, said diner owner Iskender Kangal.
Kangal, whose family has owned the diner for almost 14 years, said he had closed for the night at 10:30 p.m. Thursday.
Shortly after 4 a.m. he was awakened by a telephone caller telling him that his business was in flames.
"By the time I got there, it was all gone, burned to the ground," Kangal said.
No serious injuries were reported. One firefighter was treated for an ankle injury at the scene, McClain said.
The fire is under investigation by the Burlington County Fire Marshal's Office. The cause of the blaze and its point of origin were not known.
McClain said the diner had served as an unofficial meeting place for firefighters.
"It really was a staple of the community," he said. "The guys and myself would hold informal meetings there. The coffee was great, and the food was pretty good, too."
Kangal said he and his brother Cavit plan to reopen the diner at the same location.
