SINGAPORE - Slightly hazy conditions are expected on Sunday, the National Environment Agency (NEA) said in an update on Saturday evening.

"The 24-hr PSI for the next 24 hours is expected to be in the high end of the moderate range and the low end of the unhealthy range, and may enter the mid-section of the unhealthy range if denser haze is blown in," NEA said in the statement issued on Saturday evening.

It added that visibility could be reduced if denser haze is blown in.

The 24-hour Pollutant Standards Index (PSI) was in the moderate range throughout Saturday. As of 6pm, the 24-hour PSI was 79 to 87. The three-hour PSI stood at 84.

Moderate to dense smoke haze is still persisting in central and southern Sumatra and some haze has spread to the sea areas to the south and west of Singapore, NEA said.

In addition, some haze from Kalimantan has spread to the sea areas far south of Singapore.

Planes from Malaysia and Singapore arrived in Sumatra on Saturday and will soon begin water-bombing areas with forest and agricultural fires, AFP quoted Sutopo Purwo Nugroho, a spokesman for Indonesia's disaster mitigation agency, as saying.

Given the air quality forecast, healthy persons should reduce prolonged or strenuous outdoor physical exertion.

The elderly, pregnant women and children should minimise prolonged or strenuous outdoor physical exertion, while those with chronic lung or heart disease should avoid prolonged or strenuous outdoor physical exertion.

Persons who are not feeling well, especially the elderly, children, and those with chronic heart or lung conditions, should seek medical attention.

For updates, visit the NEA website (www.nea.gov.sg), the haze microsite (www.haze.gov.sg), follow NEA on Facebook (www.facebook.com/NEASingapore) and NEA Twitter (@NEAsg), or download the myENV app.