The National Environment Agency said a wind change had caused the smoke from the fires on Indonesia's Sumatra island to drift towards Singapore, lifting the government's pollution standard index from "good" to "moderate".

"The impact on Singapore has not been bad so far but the prevailing winds are changing to a more south-westerly direction and beginning to blow the smoke haze towards Singapore," the agency said in a statement, adding there was a distinct burnt smell in the air throughout the city-state.

The agency said hazy conditions were expected to remain in Singapore for the rest of the week, although it was unlikely the pollution would reach unhealthy levels.

Malaysia, to the north of Singapore, has already been hit by the haze, with the government there warning on Wednesday schools may have to be closed to stop children from going outside and breathing the air.

The burning of forests in Indonesia, mainly to clear land for cultivation, frequently causes environmental problems in other Southeast Asian nations with the practice continuing despite it being outlawed.

In 1997 and 1998, haze caused by forest fires in Indonesia caused serious health problems and disrupted airline schedules throughout large sections of the region, including in Singapore, Malaysia and the Philippines.

The haze then caused an estimated 9.3 billion dollars in economic losses.

TERRA.WIRE