Aircraft operations in Sarawak were threatened today as air quality and visibility worsened badly due to open burning on plantations, officials said.

Authorities in Sarawak state distributed 1.3 million face masks as the haze began to take a toll on people's health, with a sharp rise in asthma, conjunctivitis and respiratory tract infections.

The Air Pollutant Index showed six areas had soared into the unhealthy range of 101-200, the Department of Environment said.

In Kuching the index reached 157, while Sibu posted 151 and the towns of Samarahan and Sri Aman edged up to 149 and 134 respectively. Visibility dropped to below one kilometre in Kuching, 1.8km in Sri Aman and 3km in Bintulu.

An official at the Meteorological Department told AFP that normal visibility was 10km and anything below 4km posed a risk for air travel and could disrupt flight operations.

"As standard practice, we release an advisory to the various airports but it is at their discretion whether or not it's safe to fly," he said.

API in KL 'moderate'

The official said that peninsular Malaysia had escaped the worst of the haze this week due to the southwest monsoon which was blowing the smoke and dust in a different direction.

The air pollutant index in west Malaysia remained mostly moderate with the capital Kuala Lumpur posting a reading of 64.

Burning in Indonesia and some parts of Malaysia to clear land for crops causes an annual haze that afflicts Malaysia, Singapore and Thailand as well as Indonesia itself.

Sarawak today banned all open burning with immediate effect as the haze began to take a toll on health, the official Bernama news agency said.

The state's deputy chief minister George Chan said hospitals had reported a sharp rise in the number of haze-related ailments, and that the surgical masks would be distributed particularly to those working outdoors.