Air pollution in part of Singapore hit the country's "very high" band on Wednesday while East Timor shut schools, as haze from forest fires raging in Indonesia causes a regional crisis.
In Indonesia, authorities said more than 280,000 respiratory problems have been recorded in haze-affected regions since August 18, as blazes burned through hundreds of thousands of hectares of forests and plantations on Borneo and Sumatra islands.
Air pollution in western Singapore on Wednesday hit "very high" -- the country'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.
Singapore's National Trades Union Congress said Monday that public transport workers and delivery riders could receive free N95 masks, but AFP found uptake was slow.
"It's a little bit uncomfortable to wear a mask, and some orders we have to walk around blocks, or park outside," a delivery rider who gave his name only as Daniel told AFP.
"With the mask, I will have to breathe heavier," the 27-year-old said.
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.
On Sumatra island, a fire razed nearly 300 homes, forcing hundreds of people to evacuate, an official said Tuesday.
Residents first spotted the fire approaching their village in Bangka Belitung province on Saturday and tried to put it out themselves with portable water pumps.
But the fire continued to smoulder underground in peatland, and when the wind shifted, the flames moved towards their homes.
The local disaster agency said nearly 1,000 people fled the village.
"My house is gone," Leni, a 55-year-old villager now staying at a shelter with her family, told AFP.
"There's nothing left. I could only save myself and take my kids with me... I panicked and didn't have the time to grab anything," said Leni, who like many Indonesians has one name.
President Prabowo Subianto on Monday ordered the government to mobilise maximum efforts, with officials saying more than 60,000 personnel had been deployed to combat fires on the ground.
But efforts so far, including cloud seeding and water-bombing, have had limited success.
Malaysia has been in talks with Indonesia to explore how the two countries can cooperate, Foreign Minister Mohamad Hasan said on Wednesday.
"The form of cooperation will depend on the outcome of the discussions, but the authorities of both countries have... begun talks on how we can work together to tackle the haze, which appears to be getting worse," Mohamad told the Bernama national news agency.