The American Museum of Natural History was evacuated Friday afternoon because of a smoke condition inside the iconic building.
Over 3,000 museum attendees and workers poured out onto the street on Manhattan's Upper West Side as firefighters arrived to battle the blaze.
FDNY officials said the fire started at around 3:30 p.m. when a maintenance worker using a blow torch outside the building caused an air conditioning unit to catch fire. The building's heating, ventilation and air conditioning system then sent smoke into the museum.
Eyewitnesses said they saw smoke coming out of light fixtures on the first floor of the museum and then the sprinklers go off.
There were no reports of any injuries.
By 4:30 p.m., officials said the fire had been knocked out and that museum workers were being allowed to reenter the building. It remained closed to the public and an event planned for Friday night had been canceled, the museum's website said.
Museum officials said they were still assessing the extent of the damage inside the museum, which included water damage from the sprinkler system.
The museum is expected to reopen Saturday.