"This could lead to drier periods and the possibility of escalating hot-spot activities during the coming dry season," environment ministers from Malaysia, Indonesia, Thailand, Singapore and Brunei said in a statement.

La Nina refers to an abnormal cooling of sea surface temperatures in the Pacific Ocean, while its counterpart El Nino refers to a warming of surface temperatures.

Since 1997, peat and forest fires in Indonesia's Sumatra and Borneo islands have triggered a choking haze which billows across the region, affecting Singapore, Malaysia and parts of Thailand.

The ASEAN ministers had gathered in the Malaysian administrative capital to discuss the haze, which usually occurs around mid-year as farmers and timber and plantation firms in the region openly burn plots of land ahead of the planting season.

ASEAN, the Association of Southeast Asian Nations, groups the countries of Malaysia, Indonesia, Thailand, Singapore, Brunei, Cambodia, Laos, Myanmar, Vietnam and the Philippines.

"We have to prepare for the worst and hope for the best," Indonesian Environment Minister Rachmat Witoelar told reporters.

"We are not going to delude ourselves that we are going to wipe out all the haze. There will be some burning, some haze."

Near-annual bouts of haze have made many people ill across a wide area of Southeast Asia, cost local economies billions of dollars and badly hit the tourism and airline sectors.

Singapore appealed to tourists not to avoid the region during the period as has happened in the past.

Southeast Asia is a magnet for big-spending visitors from the Middle East in July and August, as they seek to escape the scorching summer back home.

"Please come and visit the region," Singapore Environment Minister Yaacob Ibrahim said.