The fire, which was fully extinguished by 2:30 p.m., left "extensive damage" to the east porch of the clubhouse, according to Mr. King.
There were a few minor injuries reported, though none required medical attention, Mr. King noted.
Mr. King said the fire was under control just before 2 p.m. on Wednesday.
Southampton Fire Department Public Information Officer Don King said that more than 100 firefighters are on the scene working to put out the clubhouse fire.
"It's contained, but we still have to do some work on it," Mr. King said of the fire.
The following fire departments responded on Wednesday: Southampton, North Sea, Bridgehampton, Hampton Bays, East Quogue and Westhampton.
The East Hampton, Shelter Island and Sag Harbor fire departments are on stand by.
Mr. King confirmed that the fire appeared to start in the roof and is now contained in the east wing.
Fire trucks are situated on Sebonack Inlet Road pumping water from Bullhead Bay to put out the fire in the iconic main clubhouse.
Firefighters were transporting the water up a hill and through the old gates outside the clubhouse to douse the fire in the east wing of the building, according to witnesses on the scene. The gates are apparently too narrow for a fire truck to fit through.
The golf course was founded in 1908.
Crowds of employees and thick smoke surrounded the clubhouse on the golf course, founded in 1908, on Wednesday afternoon.
A fire was reported at the National Golf Links of America in Tuckahoe late Wednesday morning.
Southampton Town Police were called about a fire on the roof of the clubhouse building at 11:34 a.m., according to Town Police Sergeant Michael Burns.
No injuries were reported as of Wednesday morning.
Additional information was not immediately available.