Deputy Director of Public Health in Sarawak's health department, Andrew Kiyu, said government clinics monitoring medical problems in hazy conditions had reported a "higher than average" number of asthma cases.

The clinics had been checking for cases of acute respiratory tract infections, conjunctivitis and asthma, he said.

"Out of the three, it seems that asthma is a more sensitive indicator. In that sense in some places it shows a relative increase in the number of asthma cases," Kiyu told AFP.

State officials have said they will soon start cloud seeding activities to counter the pall of smoke blamed on fires in Indonesia's neighbouring Kalimantan on Borneo and some fires in Sarawak.

Data from the environment department Tuesday morning showed air quality in seven areas in Sarawak at unhealthy levels of between 100 to 200 on the Air Pollutant Index (API).

The worst hit area was Sarikei, where air quality was pushing very unhealthy levels at 196. The API deems a reading of 101 to 200 as unhealthy, and 201 to 300 as very unhealthy.

Air quality was also at unhealthy levels in the southern coastal area of Tawau in Malaysia's neighbouring Sabah state, which is a transit point for tourists travelling to nearby dive spots.

Kiyu said authorities had advised Sarawakians in haze-hit areas to limit their outdoor activities, and would recommend masks if the API went above 200.

However, he said it was "unlikely" Sarawak would see air quality deteriorate to the same levels as 1997, when the API hit 800.

The 1997-98 haze crisis cost the region an estimated 9.0 billion dollars by disrupting air travel and other business activities.