This aerial photo taken from a commercial aircraft shows haze
This aerial photo taken from a commercial aircraft shows haze from Indonesian forest fires blanketing a bridge in Kuching, the capital city of Malaysia's Sarawak state on the island of Borneo on September 5, 2026. Indonesia has for weeks been fighting wildfires blanketing parts of Borneo and Sumatra with smog, with haze also contributing to air pollution in Malaysia, Singapore, and the Philippines. Mohd Rasfan / AFP via Getty Images

Malaysia has declared an emergency in the Sarawak district of Serian after its Air Pollutant Index reached 521 on Friday, the first reading above the threshold at which the country's scale registers an emergency.

King Sultan Ibrahim Iskandar consented to the declaration, according to a statement from Prime Minister Anwar Ibrahim's office. Serian is an agricultural town of just under 90,000 people near the border with Indonesia's Kalimantan.

Kuching, Sarawak's capital and a far larger city, recorded 311 the same day — within the hazardous band.

What the number means

Malaysia's index runs in bands: 0 to 50 is good, 51 to 100 moderate, 101 to 200 unhealthy, 201 to 300 very unhealthy, 301 to 500 hazardous, and above 500 an emergency.

The thresholds carry automatic consequences. Outdoor school activity stops at 101. Schools, along with tadika and taska, close once the index touches 200 — so schools across affected parts of Sarawak have been shut for some time already. Above 500, officials have said, non-essential work and outdoor activities can be halted. The prime minister's office did not detail what the Serian declaration will involve.

⚠️ One technical point matters for interpreting any of these figures. The index's particulate sub-index is a rolling 24-hour average. It therefore lags a fresh smoke plume, and a reading of 521 describes conditions over the preceding day rather than the moment it was published. Live PM2.5 readings from monitoring apps will move first.

How fast this escalated

The trajectory is the part that is hard to look away from.

In early August, Serian was recording an API of about 185 — unhealthy, but not exceptional for the season. On the morning of Sept. 1, six Sarawak locations were above 300: the monitoring station at Serian district police headquarters read 408, Kuching 407, Samarahan 372, Sri Aman 361, Sarikei 333 and Sibu 309. Mukah, Bintulu and Samalaju were in the very unhealthy band at 234, 232 and 225.

Three days later, Serian was at 521.

Earlier in the season the haze had already reached the peninsula, with Sri Aman recording 218 on Aug. 28 and unhealthy readings appearing in Selangor.

Where the fires are

Attribution in a haze episode is usually contested. This year's hotspot counts are not especially ambiguous.

The ASEAN Specialised Meteorological Centre, the regional haze monitoring body hosted by Singapore since 1993, counted 643 hotspots in Kalimantan and 17 in Sumatra on Aug. 8, against 25 across Malaysia — 22 of them in Sarawak. Smoke plumes from West and Central Kalimantan were drifting north into western Sarawak.

Hundreds of hotspots upstream against dozens domestically is the characteristic shape of a transboundary episode rather than a local one.

Peat makes it worse and more persistent. Drained peatland burns below the surface, smoulders for weeks, resists rainfall and produces disproportionate quantities of fine particulate. That is why rain over Malaysia offers only temporary relief — it washes particulate from the air without touching the source.

The regional picture

Indonesia has temporarily closed hiking access across nine national parks considered vulnerable to fire, and heavy haze around Supadio International Airport in West Kalimantan forced 10 commercial flights to be rescheduled on a single morning this week. Water-bombing operations were carried out on Saturday to stop fires spreading near the new capital at Nusantara.

Jakarta says it continues to coordinate with neighbouring countries and to use ASEAN mechanisms on transboundary haze while intensifying domestic fire control.

The effects have reached further than Borneo. Quezon City in the Philippines suspended face-to-face classes in all public schools on Sept. 1 after its monitoring network recorded pollution from very unhealthy to acutely unhealthy levels, saying the deterioration could possibly be connected to the Kalimantan fires.

Some AirAsia flights have been flagged as facing possible cancellation.

Precedent

Malaysia has been here twice at this scale. In August 2005 a state of emergency was declared in Kuala Selangor and Port Klang after readings exceeded 500, closing schools in the affected areas. In October 2015, close to 7,000 schools shut nationwide as readings reached hazardous levels.

Between those episodes and this one sit more than two decades of ASEAN agreements on transboundary haze, and an emergency declaration in a Malaysian town caused by fires in another country.

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