Flames broke out just after 1:00 Friday at Akasaka Japanese restaurant in Wallington. Firefighters comforted each other at the scene.
Fire officials say 57-year-old Gregory Barnas was on the roof at the time. Sources tell Eyewitness News he fell and went into cardiac arrest.
Barnas started his work with the Wallington Fire Department as a junior firefighter in 1972.
"It's a tragic loss for our fire department, words just can't even come to mind for it," said friend and fellow firefighter Mark Tomko.
Bergen County Prosecutor John Molinelli says Barnas' sons are both firefighters who were at the scene of the fire when their father fell.
Molinelli says the fire is being investigated but that it does not appear suspicious.
The cause of the blaze remains under investigation.