Singapore's air quality reached its worst levels in over a decade on Wednesday as haze from Indonesian wildfires intensified. The one-hour PM2.5 reading in the western part of the city-state climbed to 288 micrograms per cubic meter, entering the National Environment Agency's "very high" category for the first time this season.

The spike marks the highest hourly reading since the severe 2015 haze crisis, when levels briefly hit 471. Other regions also saw elevated readings, with the 24-hour Pollutant Standards Index remaining in the unhealthy range across the island. Singapore, Kuala Lumpur, and Medan ranked among the world's most polluted cities that afternoon.

The haze stems primarily from land-clearing fires in southern Sumatra and Kalimantan, where Indonesia battles its worst wildfire season in 11 years. Dry conditions fueled by a strong El Niño have allowed blazes to burn out of control, sending smoke plumes drifting under prevailing winds. Indonesian authorities reported over 280,000 respiratory cases linked to the fires since August.

Neighboring areas felt the effects sharply. East Timor closed schools nationwide for three days starting Thursday to protect students and staff. Several Malaysian states also shut schools, while respiratory illnesses rose across the affected zones.

Singapore responded with subsidies for haze-related medical treatments, a measure last used in 2015. Officials indicated N95 masks would be distributed to vulnerable groups if conditions worsen further. The National Environment Agency advised residents to limit outdoor activities, especially the elderly, children, and those with heart or lung conditions.

The episode highlights ongoing challenges with transboundary pollution in Southeast Asia. Singapore has faced repeated haze events tied to Indonesian practices, prompting diplomatic pressure for better fire prevention and enforcement. Indonesia recorded thousands of hotspots this month, the most in October since 2015.

Forecasts suggest unhealthy air quality could persist as dry weather continues in fire-prone areas. Residents continued daily routines under the haze, though visibility dropped and many wore masks outdoors.