KUALA LUMPUR — Smoke from forest and peatland fires burning across Indonesia has pushed air quality in parts of Malaysian Borneo to hazardous levels, driving a surge in respiratory illness and forcing the cancellation of outdoor Independence Day celebrations, Al Jazeera reported.

The smoke, drifting from fires in Kalimantan in the Indonesian portion of Borneo, has settled over the Malaysian state of Sarawak for much of August, and has also reached peninsular Malaysia, Brunei and Singapore. It is the region's worst haze episode since 2015, when fires in Indonesia exposed tens of millions of people to toxic smoke and left more than 500,000 people with respiratory ailments.

On Tuesday, six areas in Sarawak recorded hazardous air quality, with readings above 300 on Malaysia's Air Pollutant Index; anything above 100 is considered unhealthy. In Kuching, the state capital, the index reached 407, while in Serian, a town near the Kalimantan border, it hit 408.

A health system under strain

Malaysia's health ministry reported a sharp rise in illness nationwide. In the week of 23 to 29 August, asthma cases climbed to 1,811 from 219 the previous week, while conjunctivitis cases rose to 720 from 146.

Karen-Michaela Tan, an asthma patient living near Kuala Lumpur, said she had been "wheezing audibly" last week and feeling "breathless when climbing the stairs", and needed two nebuliser treatments in succession along with a heavy dose of steroids. "Doctors are erring on the side of caution when it comes to asthma patients, choosing to up dosages rather than risk a patient being hospitalised for shortness of breath," she told Al Jazeera.

The Association of Southeast Asian Nations has activated a Level 3 transboundary haze alert, its highest, for the southern part of the region, citing rising fire hotspots and prolonged dry weather driven by an intensifying El Nino pattern.

Closures and cancellations

Sarawak cancelled its outdoor Independence Day celebrations on Monday, and officials warned that further restrictions could follow. Deputy premier Douglas Uggah Embas said any area where readings cross 500 would be placed under a local emergency, with all public and private offices closed. "Only essential services will be allowed to operate," he said.

Under education ministry rules, outdoor activities are suspended when the index reaches 100 and schools must close at 200. On 20 and 21 August, nearly 600 schools in and around Kuching shut, affecting some 200,000 pupils, and on 28 August a further 30 schools in Sarawak closed, keeping more than 4,000 children at home.

Across the border

Indonesia's deputy health minister, Dante Saksono Harbuwono, said about 13,500 people were treated for respiratory infections in July and August, and roughly 5.5 million people on Borneo and Sumatra had been directly exposed to smoke.

Indonesian government figures show that fires between January and July burned more than 200,000 hectares (about 494,000 acres) across the two islands, with nearly 95,000 hectares burning in July alone. Hotspots in West Kalimantan nearly doubled on Monday, rising by 3,553 to 7,377, said Berton Panjaitan of Indonesia's National Disaster Mitigation Agency, while in Central Kalimantan hotspots fell by 147 to 5,244.

Analysts say the fires are largely set deliberately, with plantation companies and smallholders clearing rainforest and carbon-rich peatland for palm oil, farming and pulp production. The practice is illegal, and Indonesian police said last week they had arrested 72 people suspected of setting recent fires.

Helena Varkkey, a specialist on transboundary haze at Universiti Malaya, said El Nino appears headed for "super" strength, and that "the intensifying El Nino means hotter and drier conditions", so "any fires that happen will have a bigger and longer regional impact". Peat fires are particularly stubborn: what looks extinguished on the surface can smoulder underground for weeks, and only sustained rain will soak the soil enough to put it out.

Reporting attributed to Al Jazeera. Air quality readings and health figures are those published by Malaysian and Indonesian authorities.