The fire was reported at 1:22 p.m. on the ground floor of a three-story building near the intersection of Jackson and Front streets.
Yong Chong, an employee at Cafe Insalata, said smoke was coming from a restaurant across the street, Kokkari Estiatorio, located at 200 Jackson St.
Fire department spokeswoman Mindy Talmadge said the flue runs all the way to the top of the building, and although firefighters also found fire in the flue space on the top floor, the flames did not extend into the building.
The blaze was extinguished at 2:04 p.m., she said.
The building was safely evacuated while crews fought the fire, and no injuries have been reported, Talmadge said.
