NAKHON SI THAMMARAT - A vast fire is still burning in the Phru Khuan Khreng peat swamp forest in this southern province, defying firefighters' efforts three days after it erupted.

The Public Relations Office of Nakhon Si Thammarat reported the latest state of the fire on Sunday, saying it was expected to be under control within a few days unless a strong wind moves in.

Firefighters had control of the blaze in many areas, including Ban Khuan Yao, the statement said.

The Ministry of Naturual Resources and Environment on Sunday deployed a helicopter to make an aerial survey and determine the full extent of the fire, which is in Thailand's second largest peat swamp forest.

The fire has already damaged about 300 rai, nearly half a square kilometre, in Cha-uat district on the outskirts of seven villages.

The Phru Khuan Khreng peat swamp is on the eastern side of the South and extends over roughly 313 square kilometres of Nakhon Si Thammarat, Phatthalung and Songkhla provinces.

The peat swamp fire as seen from a helicopter on Sunday. (photo supplied)