SINGAPORE - It is another hazy day for Singapore on Tuesday (Sept 15) as the air quality continues to hover within the unhealthy range despite a brief downpour in the late morning.

Heavy showers at around 11am till noon provided a brief respite, but the air quality continued to be in the unhealthy range for the afternoon.

As of 11pm, the 24-hour Pollutant Standards Index (PSI) was between 108 and 127. The unhealthy range is 101-200. The three-hour PSI, an indicative reading not tied to health advisory, was 108 at 11pm, after crossing the 200-mark on Monday night. If the air quality stays above 200 for 24 hours, it would be considered very unhealthy (201-300).

The National Environment Agency (NEA) said on Tuesday evening that the 24-hour PSI is predicted to be in the mid to high sections of the unhealthy range but may deteriorate into the low section of the very unhealthy range on Wednesday if denser haze from Sumatra is blown in.

Four hotspots were detected in Sumatra on Tuesday. The low count was due to partial satellite pass and cloud cover, NEA said in an update at around 8.30pm.

Some schools have cancelled or moved outdoor activities indoors as the haze situation continues to worsen.

Indonesia has declared a haze emergency in Sumatra's Riau province, as the choking smoke surged way past already hazardous levels and forced thousands to flee Pekanbaru, Riau's capital, which is about 280km away from Singapore.

In Malaysia, the authorities on Tuesday ordered school closures in Kuala Lumpur and neighbouring states where air pollution indices were in the upper range of "unhealthy" and nearing "very unhealthy". More than half of Malaysia's 52 monitoring stations registered "unhealthy" air on Tuesday.