SINGAPORE: The Pollutant Standards Index (PSI) in Singapore may enter the unhealthy range if the haze situation in Indonesia's Sumatra persists or worsens, said the National Environment Agency (NEA) on Tuesday (Sep 10).
As of 8pm on Tuesday, the 24-hour PSI was in the moderate range of between 85 and 96. A PSI reading of between 101 and 200 falls in the unhealthy range.
The 1-hour PM2.5 concentration readings were in the normal range at 8pm.
"Overall, the PSI for the next 24 hours is forecast to be in the high end of the Moderate range," said NEA in a media advisory.
"Depending on wind conditions, the PSI may enter the unhealthy range if the haze situation in Sumatra persists or worsens."
A total of 537 hotspots were detected in Sumatra on Tuesday, a sharp increase from the 380 reported on Monday.
"Moderate to dense smoke haze continued to emanate from persistent hotspots in Riau and Jambi provinces," said NEA.
In addition, 749 hotspots were detected in Kalimantan, the agency added.
Forest fires have raged through parts of Sumatra and Kalimantan in recent weeks, prompting the Indonesian government to send in thousands of military and police to douse the flames.
The country’s neighbours have regularly complained about haze caused by such forest fires - often started by farmers trying to clear land for palm oil and pulp plantations.
In Malaysia, air quality has dropped to "unhealthy" levels in and around Kuala Lumpur, according to the government's air pollutant index, and the skyline has been shrouded in thick smog.
Around 400 schools were closed on Tuesday in nine districts of Malaysia's eastern Sarawak state, with more than 150,000 students affected, according to the local education department.
READ: Malaysia sends half a million face masks to haze-hit Sarawak as 409 schools close
But Indonesia's climate agency BMKG on Tuesday disputed Malaysia and Singapore's reports that smog in their countries was from its forest fires.
Its chairwoman told a news conference that fires had also been spotted in Malaysia, the Philippines, Papua New Guinea, Vietnam, East Timor and Thailand.
The 2015 fires in Indonesia were the worst for two decades, choking the region in haze for weeks.
President Joko Widodo last month warned that officials would be sacked if they failed to stamp out forest fires.