Haze from fires burning in Indonesia has drifted over Malaysia's west coast, sending air pollution to dangerous levels in one town where schools were reportedly forced to shut on Wednesday.
In Muar, a coastal town on the narrow strait which separates the two countries, pollution levels shot up to 415 by Wednesday morning, well into the hazardous range which begins at 301. A rating of 0-50 is considered good.
"This is because of a hot-spot from Sumatra. You can see the affected area on satellite images, it's caused by land clearing and plantations," an environment department official said.
Education Minister Muhyiddin Yassin said schools in Muar had been closed and thousands of masks were being distributed, according to the Star daily. Authorities were also rushing to carry out cloud seeding to disperse the smoke.
Muar is situated in Johor state, where most other towns were not so badly affected. However in the west coast tourist centre of Malacca, air quality had deteriorated to 106, which is in the "unhealthy" range.
Haze caused by fires in Indonesia builds up during the dry season, affecting tourism and contributing to health problems across the region.
Indonesia's government has outlawed land-clearing by fire but weak law enforcement means the ban is largely ignored.