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 there.
"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.
Neither Palanivel nor the prime minister's office could be reached for comment.
A spokesman at the Johor state operations centre told Reuters that it was awaiting orders from the National Security Council and that residents in the affected areas should stay indoors.
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.