Singapore's environment agency issued a health advisory today as a thick haze from fires in Indonesia choked the city-state and surrounding region.

Singapore's three-hour-average pollution index peaked at 130 mid-morning before dropping back at 0600 GMT to a moderate 91. A reading above 101 is considered unhealthy.

"Persons with existing heart or respiratory ailments should reduce physical exertion and outdoor activity. The general population should reduce vigorous outdoor activity," the National Environment Agency advised.

The fog-like haze, which has affected Singapore for several days, carried with it a burning smell.

In neighbouring Malaysia, pollution also worsened as readings from the Department of Environment showed air quality at unhealthy levels in 20 areas of the country, up from 12 yesterday.

"The smoke haze situation has deteriorated overnight. The prevailing winds have remained southerly to southwesterly overnight and they have brought smoke haze from southern Sumatra to Singapore," a statement from the city-state's environment agency said.

An agency spokeswoman told AFP the highest three-hour-average pollution reading ever recorded in Singapore was 226 in 1997 - well above today's levels. The highest daily 24-hour average was 142 recorded in 1994. Yesterday's level was 80.

Singapore's environment agency said latest satellite pictures showed 506 hotspots - large areas with high temperatures indicating fires - and thick smoke haze in Indonesia's Sumatra island, mainly in Riau, Jambi and South Sumatra provinces.

"The prevailing winds are transporting the smoke haze towards the Malacca Straits, Peninsular Malaysia and Singapore," the agency said.

Hotspots in Borneo

Indonesian officials reported 1,496 Sumatran hotspots and 2,075 in Kalimantan, Indonesian Borneo, yesterday.

"In Kalimantan, only around 60 to 70 percent of the hotspots can be detected by the satellite because of the thickness of the haze," an official from the government forest fire monitoring unit told AFP.

Poor visibility of 50 to 100 metres (55 to 110 yards) in Palangkaraya, capital of Central Kalimantan province, stopped all flights in the morning, said Hidayat, an official from the local meteorological office.

A spokesman for Singapore's Changi Airport said today the haze had not affected operations at the regional aviation hub.

In Indonesian Borneo, hundreds of firefighters, aided by police and volunteers, were Friday dousing illegal forest fires causing acrid haze that blanketed western parts of the island, officials said.

Residents in the southern Thailand provinces of Narathiwat and Yala, which border Malaysia, reported clear skies and fine visibility on Saturday.

Malaysia's meteorological department said it expected conditions to improve over the weekend in Sarawak as well as Sabah state and the country's north.