The fires -- usually started by illegal burning to clear land for farming -- have unleashed choking haze across Southeast Asia.  (Photo: AFP)

BANGKOK (Xinhua) -- The Thai Pollution Control Department on Sunday said if the Indonesian haze which now covers Thai south goes beyond PM2.5 level 90, the department will issue red alert.

The current PM2.5 level is at 70, according to the department.

Meanwhile, the Hat Yai municipality on Sunday endured the thickest haze from the current spate of Indonesian forest fires, while levels of PM2.5 reached the dangerous bracket in Trang and Satun provinces, said the department.

The department reported the level of PM2.5 in the southern business and tourism city to be 79 microgrammes per cubic metre of air on Sunday, the highest level since the current outbreak began.

Satun Province was the second-worst-hit area, with the small particle reading rising to 66 from 39 on Saturday, while the PM2.5 level in Trang breached the safety threshold for the first time, hitting 52 on Sunday.

The Songkhla Provincial Public Health Office warned all residents in its province that "Outdoor activities should be curbed and people should wear face masks when they leave home. All doors and windows should be shut to prevent haze entering the house."

Thai TV showed footage of officials at the Songkhla Zoo spraying water into the air to alleviate the haze for animals.