SINGAPORE - After a brief respite on Friday (Sept 11) when Singaporeans went to the polls, slightly hazy conditions returned on Saturday (Sept 12) afternoon.

The three-hour Pollutant Standards Index (PSI) reading crept up steadily through the morning, peaking at 147 at 4pm. It dipped down to 129 at 7pm.

As at 7pm, the 24-hour PSI - a measure of air pollution - stood at 83-97.

Air quality is considered to be in the unhealthy range when the 24-hour reading falls between 101 and 200.

The National Environment Agency said in an update at 5pm that the conditions were due to haze from Sumatra being blown in by the prevailing winds. This is expected to persist for the rest of the day and on Sunday.

On Thursday, Singapore was hit by the worst haze since April last year, with the three-hour PSI crossing into the "very unhealthy" band.

It prompted Environment and Water Resources Minister Vivian Balakrishnan to register his deep concern of the deteriorating situation to his Indonesian counterpart, Minister of Environment and Forestry Siti Nurbaya Bakar, after the number of hot spots in Sumatra rose alarmingly.