The BBC's Frances Harrison: "Satellite tracking is showing between 200 and 300 hot spots."

Meteorologists in Singapore have warned of air pollution levels verging on the unhealthy, and officials in Malaysia have confirmed the presence of haze in many parts of the country.

In 1997, smoke from slash and burn land clearing, mostly in Indonesia, caused an environmental disaster that is estimated to have cost the region $4bn.

Satellite tracking is showing between 200 and 300 hot spots, indicating forest fires are burning on the islands of Borneo and Sumatra.

Officials in the Indonesian province of West Kalimantan in Borneo have already issued health warnings telling people to use face masks, as they say an unknown number of fires are burning out of control.

Slash and burn land clearing is being blamed

In Singapore, air pollution readings have risen, prompting an increase in complaints with those with respiratory problems.

But in neighbouring Malaysia, the authorities stopped publishing the country's air pollution index in June as concern grew that the haze might be coming back.

The country's environment minister accused the foreign media of using air pollution to scare away tourists.

Choking smog

At its most severe, the haze phenomenon in 1997 reduced visibility so much that air flights were cancelled and children and the elderly had to stay indoors because of the choking smog.

Traditionally, small farmers in these areas clear land by clearing the jungle and setting it on fire.

But environmentalists think the haze problem is caused by commercial plantations using slash and burn methods to clear bigger tracks of the rain forest during abnormally dry weather.

In 1997, the region lost billions of dollars in tourism revenues, but correspondents say the situation this year has not yet reached those levels.