Fires burning in central Sumatra have once again blanketed Singapore in a haze that has pushed up pollution levels in the city-state famed for its "clean and green" image. Parts of Malaysia have also been affected.

Satellite pictures showed "hot spots" in the Indonesian province since Monday, with winds blowing the smoke to Singapore and sending the pollutant standards index up to 74, the highest in months.

The Malaysian peninsula was also "very much in the path of the haze," said Emmanuel Nabet, of satellite operator Spot Asia.

Fires of such size and intensity have not been seen since March last year and could have been started by plantation and logging companies. With the rainy season over, the companies are no longer hampered by wet weather.

Health warnings would only be issued if the index reached 100, the Environment Ministry said. Although the haze was likely to remain for the next day or two, environmentalists said the conditions were expected to improve with a change in wind direction.

Fires raging in East Kalimantan and Sumatra forests and brushlands during 1997 and 1998 resulted in staggering health and tourism losses in Indonesia and the region.