SINGAPORE - Air quality deteriorated further on Tuesday afternoon after entering the unhealthy range at 11am.
At 5pm, the 24-hour Pollutant Standards Index (PSI), a measure of air quality here, ranged between 91 and 106.
The elderly, pregnant women and children are advised to minimise prolonged or strenuous outdoor activity, while those suffering from chronic lung or heart disease should avoid these activities when the 24-hour PSI exceeds 100.
The National Environment Agency (NEA) said the hazy conditions are caused by smoke haze from Sumatra, blown in by the prevailing winds from the south and southwest.
The hazy conditions are expected to persist for rest of Tuesday and continue into Wednesday.
The NEA said the 24-hour PSI for the next 24 hours is expected to be in the low to mid end of the unhealthy range (101 to 200). The agency warned that it may deteriorate further if the winds are unfavourable.
Thundery showers are forecast for Wednesday morning.