Persistent rains have cleared the air across vast stretches of Southeast Asia that have choked for weeks on hazardous smoke from Indonesian fires, with officials and citizens expressing hope on Thursday that the crisis could soon end.

Parts of Indonesia, Malaysia and Singapore enjoyed the cleanest air in two months, while affected areas of the Philippines and Thailand also gained a respite from pollution that has sickened hundreds of thousands, disrupted air travel and fueled anger at Jakarta.

"We can see clouds again!" Singapore Defense Minister Ng Eng Hen gushed in a Facebook posting that included a picture taken from his office of now-unfamiliar blue skies.

"I am sure that all of us in Singapore woke up this morning and felt so good that we had clear blue skies again."

Malaysia's top weather forecaster declared the region's rainy season - crucial to putting out the annual outbreak of smoke-belching Indonesian forest and agricultural fires - had begun.

"We should have blue skies and no more haze," Che Gayah Ismail, director-general of the country's meteorological department, told AFP, adding that any further smoke would be blown away from the region.

The fires and resulting regionwide pollution occur to varying degrees each year during the dry season as vast Indonesian plantations are illegally cleared by burning.

Experts had warned that this year's outbreak was on track to become the worst yet due to bone-dry conditions caused by El Nino, which alters weather patterns across the Pacific basin.

Growing fears

Fears had grown that the rainy season could be delayed for months, prolonging the health and environmental disaster.

Indonesian authorities say 19 people have died either fighting the fires or due to the smoke, and that 500,000 Indonesians are suffering from respiratory illness.

Indonesian officials are yet to declare that the corner had been turned in the battle against the haze. But its disaster agency spokesman Sutopo Purwo Nugroho said that recent rainfall on the huge islands of Sumatra and Borneo - where hundreds of fires have smoldered since July - has dramatically reduced the smoke, and that more precipitation was expected.

Affected communities "welcomed this with joy and said grace after two months of being held captive to haze", Sutopo said in a statement.

The rains there included both natural and artificially induced showers from cloud-seeding, he added.

The crisis brings recurring pressure on Indonesia, which has failed over the years to rein in the planters accused of starting the fires.

Jakarta agreed earlier this month to accept international help after failing for weeks to douse the blazes, and has employed dozens of planes and thousands of personnel on the ground in a firefighting campaign.

Residents of Palangkaraya, an Indonesian city on Borneo where the intense fires have created eerie yellow skies and unbreathable air, expressed relief at seeing patches of blue up above.

Schools that were closed for health reasons have begun reopening, and children in uniforms were seen riding bikes without masks.