Singapore may have "occasional slight haze" for the next few days, especially in the mornings, said the National Environment Agency (NEA) in an advisory on Sunday night.

There has been thick haze blanketing parts of the Riau province in Indonesia. In Malaysia's Port Klang, air pollutant index readings on Sunday morning reached an unhealthy level of 121.

The NEA said 70 hotspots were detected in Sumatra, but wind blowing from the north-east will keep the haze away from Singapore. However, Singapore may still experience occasional slight haze due to accumulation of particulate matter under stable atmospheric conditions.

As at 9pm, the three-hour PSI or pollutant standards index, a measure of air quality, was 30. A PSI of 0 to 50 remains in the "good" range, while that between 51 and 100 is "moderate".