A smog shrouding Malaysia worsened today, delaying some flights to Indonesia and forcing authorities to consider shutting schools temporarily due to health concerns, officials said.

Malaysian environment officials blame forest fires in neighbouring Indonesia's Sumatra island for the haze.

The haze over Kuala Lumpur and the rest of the west coast has thickened due to increased open burning in Sumatra and is aggravated by hot and dry weather, an official from the Environment Department's control room told AFP .

Northern Malaysia's Penang state and the southern states of Malacca, Negri Sembilan, and Johor, along the western peninsula coast facing Sumatra, were experiencing "unhealthy" air quality, she said on condition of anonymity.

At the Batu Berendam airport in Malacca, visibility was down to one kilometre, delaying flights to Pekanbaru in Sumatra, an airport official told AFP .

Education minister Hishammuddin Hussein said he would consider closing some schools if the air quality deteriorated further.

"The safety of our children is important and we cannot take it for granted. If the haze causes harm to their health, we will ask them to stay home," he was quoted as saying by the New Straits Times newspaper.

Stop all activities

Southern Malacca state chief minister Mohamed Ali Rustam has ordered outdoor school activities to stop temporarily.

"Asthmatic patients and old folk are encouraged to stay indoors while commuters are advised to wear masks on the road as a preventive measure," Mohamed Ali was quoted as saying by the Star newspaper.

The Kuala Lumpur International Airport saw no disruptions to flight schedules despite visibility being reduced to three kilometres on Tuesday, a spokesman for Malaysia Airports said, adding that visibility improved slightly Wednesday.

In 1997 and 1998, haze caused by forest fires in Indonesia enveloped parts of Southeast Asia, including Malaysia for months -- causing serious health problems and traffic hazards and disrupting airline schedules.

The haze then caused an estimated US$9.3 billion in economic losses. -AFP