Heavy haze forced Malaysian authorities to shut schools Tuesday in three states and two key cities as aircraft were to begin cloud-seeding operations to induce rain to help clear the air.

Indonesia intensified efforts to extinguish the forest fires that cause the haze, which blanketed parts of the archipelago and neighboring countries. President Joko "Jokowi" Widodo ordered agencies to use all means, deploying more troops, to overcome the haze.

The thick, dirty white haze is an annual phenomenon mostly caused by fires illegally set to clear land for farming.

A plane equipped with chemicals to release in the air that will help clouds produce rain was due to fly over Kuala Lumpur and surrounding areas, said Maznorizan Mohamad, a meteorological department senior official. A second aircraft was scheduled to fly over Kuching in Sarawak state on Borneo island.

She said the cloud-seeding is planned for three days but will depend on cloud availability and weather conditions. The inter-monsoon season is expected to start in late September, bringing more rain over peninsular Malaysia to clear up the haze.

"It will bring temporary relief but whatever it is, we have to address the source of the problem," she said.

Indonesia's National Disaster Mitigation Agency dispatched 1,250 troops to the most stricken province of Riau on Tuesday, one day an emergency was declared due to the air quality in the peat-rich province.

The agency said 600 officers of an elite police force would follow Wednesday to South Sumatra and Jambi Central Kalimantan and Riau. Last Friday, 1,059 military personnel were sent to help snuff out fires in South Sumatra.

Some 34 of Malaysia's 52 air quality stations recorded unhealthy air levels early Tuesday. Malaysia's education ministry earlier ordered schools in Kuala Lumpur, government administrative capital Putrajaya as well as Selangor, Negeri Sembilan and Malacca states to close Tuesday.

In Singapore, air pollution reached very unhealthy levels. Organizers of this weekend's annual Formula One night race are keeping a close watch on the situation to decide whether it will be safe to race. The Singapore Grand Prix has always been held at this time of year, and while there has been some haze in past years due to the forest fires, it has never prevented the race from going ahead.