The propane tanks of the cart, stationed at Sixth Avenue, erupted in flames about 9:10 a.m., officials said.
Nearby construction workers raced over to douse the flames with a fire extinguisher, they said.
There were no reported injuries, an FDNY spokesman said.
Firefighters could be seen hosing down two scorched propane tanks in the street afterwards.
It wasn't immediately clear what sparked the fire.
Halal Guys were able to swap out the damaged cart with another to continue serving hungry customers.
Tourist Daniel Chang, 18, was eating a plate of rice and chicken when he learned about the fire from a reporter.
"Wow. It's kind of dangerous," Chang said.