A Northern Ireland Fire and Rescue Service spokesperson said they received a call about the incident shortly after 8pm on Sunday.
“Currently, 42 firefighters from stations in Ballycastle, Ballymoney and Portrush are attending,” the spokesperson said.
Local residents have been advised to keep windows and doors closed and to avoid the area.
Sinn Fein councillor Cara McShane said the fire is at the Antrim Arms, a former hotel, which she described as a “cornerstone of heritage in the town”.
“I am deeply concerned by the devastating fire at the Antrim Arms in Ballycastle,” she said.
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“My immediate thoughts are with local residents and businesses who will be affected by this incident.”
Various crews are involved in tackling the blaze, including teams from Northland, Springfield and Kilrea.
