There has been a sharp deterioration in air quality in several regions here due to the haze, since 9pm Monday night, according to the National Environment Agency (NEA).

The agency said denser haze from the sea areas south of Singapore is being blown in by the prevailing south-southeasterly winds.

As at 11pm last night, the 24-hour pollutant standard index (PSI) read was 104-152, in the unhealthy range, and the one-hour particulate matter (PM) 2.5 was 35-471 µg/m3.

NEA said the one-hour PM2.5 concentration of 471 µg/m3 in the west region was the highest recorded so far, this year.

As of 8am today, the 24-hour PSI read was 105 to 171, in the unhealthy range.

The hazy condition is expected to persist today with the 24-hour PSI to be in the low to mid sections of the unhealthy range.

NEA said the prevailing winds are forecast to blow from the southeast or south.

Reduced visibility is also expected if PM2.5 concentration levels are elevated.