The blazes in Indonesia have burned through hundreds of thousands of hectares of forest and plantations on Borneo and Sumatra islands, sickened local residents and sent thick haze across the region.
Air pollution in western Singapore on Wednesday hit “very high” – the city-state’s top level – the National Environment Agency said.
It recorded levels of tiny particulates capable of penetrating the bloodstream and lungs, known as PM2.5, at 288 micrograms per cubic metre, vastly exceeding the World Health Organization’s recommended average annual exposure of five micrograms.
Indonesia regularly battles wildfires during the dry season but has seen stronger-than-usual blazes this year as a powerful El Nino cycle brings drought.
Experts also point to slash-and-burn land-clearing practices that have changed the naturally fire-resistant landscape of Sumatra and Borneo.
The haze has drifted into neighbouring Singapore, Malaysia and East Timor, which said it would shut schools nationwide for three days from Thursday, and as far afield as the Philippines.
The closures in East Timor were necessary “as a preventive measure to protect the health of students, teachers and other members of the educational community, given current air quality conditions”, the government said.
It urged families to keep children indoors and to use “respiratory protection” if going outside.
Singapore rolled out subsidies for haze-related medical treatment from Monday, a measure last activated in 2015 when similar blazes in Indonesia cloaked Southeast Asia in toxic smoke for weeks.
The city-state has also begun distributing N95 masks to eligible residents when pollution reaches very unhealthy levels.
In Indonesia, tens of thousands of people have sought treatment for respiratory illness linked to haze from fires burning in Borneo, South Sumatra and Papua regions.
The haze has prompted Malaysia to request a meeting of regional body Asean, and on Tuesday Malaysian parliamentarian Syed Saddiq Rahman urged a “diplomatic protest”. (AFP)
