Malaysian fire-fighters are struggling to douse forest blazes that have sent smoke blowing over major towns on Borneo island.

In recent days, the pollution caused air quality to plunge to its worst level this year in parts of eastern Sarawak state on Borneo island, where more than 1,000 hectares of wildfires, are raging in several forests, especially near Sarawak's border with the neighboring sultanate of Brunei .

Malaysia 's Department of Environment readings showed air pollutant index (API) on Aug. 9 was between 122 and 197 in four areas, including three in Sarawak and one in southern Johor state.

Normally, API ranging from 101-200 is said harmful to health, and from 201-300, extremely harmful to health.

According to Malaysian authorities, hundreds of forest fires in Kalimantan and Sumatra provinces in Indonesia and Malaysian Sarawak state have seriously polluted the air.

Widespread forest fires, believed to be caused by plantation operators who set brush fires to clear land during the dry season in Indonesia and Borneo island in Malaysia , caused heavy smokes. The haze reached its worse level in 1997-1998, costing the Southeast Asian region an estimated nine billion USD due to the disruption of air travel and other trade activities./.