It is dry season in Southeast Asia and fires are again flaring, especially in the forests of Indonesia where blazes are started to clear land for plantations.

Smoke is drifting across the region, raising worries about health and economic damage, especially to tourism.

Malaysia hopes that cloud seeding, releasing chemicals such as sodium chloride and magnesium oxide into the air from aircraft, can encourage water droplets to form and rain to fall.

Jailan Simon, the director-general of Malaysia's Meteorological Department, said rain will help clear the air, but any relief will only be temporary if more smoke rolls in from Indonesian fires.

"You can reduce the severity of the haze, but cloud seeding doesn't help if there is still burning happening at the source and the wind is blowing the haze towards us," Jailan told Reuters.

There are no guarantees seeding will work.

"You need to have the right kind of clouds, the right amount of moisture in the atmosphere and the right wind conditions," Jailan said.

One of the methods used to bring rain over Malaysia is called dry seeding, which can be carried out by light aircraft at lower altitudes and over smaller areas.

The firm carrying out the seeding flights over Selangor state, AFJets, has been doing it for 10 years and boasts a success rate of nearly 90%, its firm's chief executive, Amrul Nizar Anuar, said.

Malaysia's air force carried out cloud seeding in three states last weekend, with more expected on Thursday.

Despite scattered rain following the seeding, haze conditions worsened on Wednesday.

Nearly 1,500 schools were ordered to close, affecting more than a million children, the education ministry said.

REUTERS