Malaysia declared a state of emergency in two parts of the southern state of Johor on Sunday, as smoke from land-clearing fires in Indonesia pushed air pollution above the level considered hazardous.
The illegal burning of forests and other land on Indonesia's Sumatra island, to the west of peninsular Malaysia and Singapore, to clear space for palm oil plantations is a chronic problem during the June-September dry season.
The "haze" caused by fires in Riau province on Sumatra has also shrouded neighbouring Singapore but air quality in the city state improved over the weekend after reaching hazardous levels.
"Prime Minister Najib Razak has agreed to declare emergency status in Muar and Ledang with immediate effect," Malaysian Natural Resources and Environment Minister G. Palanivel said in a Facebook post.
Palanivel said the air pollution index in the two districts had exceeded 750. A reading above 300 indicates that air pollution is hazardous. Domestic media quoted the minister as saying cloud seeding would be carried out in the affected areas.
All 211 schools in the area are to be closed until further notice, residents have been advised to stay indoors and face masks have been distributed, Khaled Nordin, chief minister of the state, said, also via posts on Facebook.
Schools have been ordered shut in the neighbouring state of Malacca, where pollution has also reached hazardous levels. Schools were also ordered to close in one district in Pahang state.
All domestic airports managed by Malaysia Airports Holdings Berhad (MAHB) are operating as usual despite the haze, the national news agency quoted the airport operator as saying.
The current visibility level of 1 km was still safe, but runways would have to close if visibility fell under 300 m, it quoted Malaysian airports official Azmi Murad as saying.
Indonesian officials have deflected blame by suggesting companies based in Malaysia and Singapore may be partly responsible. Malaysia-listed Sime Darby and Singapore's Wilmar Group both deny the charge.