Rain arrived in parts of Sumatra and Kalimantan, taking away the smoke and haze that have choked the region for weeks, and providing the provinces with much-needed but temporary relief, Indonesia's weather forecast agency BMKG said yesterday.

It rained over two days from Tuesday in six provinces affected by the fires: Riau, Jambi, South Sumatra, West Kalimantan, Central Kalimantan and South Kalimantan.

Winds blowing in from the South China Sea had contributed to the formation of rain clouds over Sumatra and Kalimantan, the agency's head of public meteorology Fachri Radjab told The Straits Times.

"The wind carried a lot of water vapour, which allowed the formation of rain clouds," he said.

Mr Fachri noted that the number of hot spots was reduced significantly as a result of the rain.

There were 3,150 hot spots across the archipelago on Monday.

But by Tuesday, the number had dropped sharply to 1,982 before slipping to 1,744 yesterday, the National Disaster Management Agency (BNPB) said in a statement.

In Riau province, which is close to Singapore, the 24-hour Pollutant Standards Index (PSI) showed air quality at midnight on Tuesday was 146, which is in the moderate range.

It improved to within the good range at 28.27 yesterday at 1pm, according to BMKG.

This is a vast improvement from Sunday when the PM10 PSI in Pekanbaru, the capital of Riau, crossed 700, entering the dangerous range and hitting a record high.

It prompted the local authorities to declare a state of emergency in the province on Monday, to fight the haze and secure more aid from the central government.

PM10 refers to particulate matter. The higher the concentration, the poorer the air quality.

The recent rain brought much-needed relief to residents of Jambi as well, with PM10 concentration readings settling at 99.57, in the moderate range, on Tuesday night, before improving further to reach 48.12 at 1pm yesterday.

Although the monsoon season is in the middle of next month, BMKG said the rain seen earlier this week will continue for the next three days over parts of Indonesia, including Riau, Jambi, West Kalimantan and the northern regions of Central Kalimantan.

The agency said the monsoon season is marked by heavy rainfall over 30 consecutive days.

Mr Fachri said clouds forming over Sumatra and Kalimantan may help efforts to induce rain through cloud seeding.

"We haven't entered the monsoon season yet but cloud seeding has sped up the arrival of rain, with more clouds for seeding," he added.

Until the recent rain, Indonesia's emergency response team has relied on four aircraft to perform cloud-seeding operations over Sumatra and Kalimantan.

Indonesia is struggling to tackle the fires engulfing Sumatra and Kalimantan, which are spreading the haze to neighbouring countries.

From January to August, fires raged across 328,724ha of land, of which 27.3 per cent was peatland, according to BNPB. In Riau, 49,266ha of land was impacted by the fires, of which more than 80 per cent of them was peatland.

Indonesia has deployed 29,039 personnel to battle the fires, with 48 helicopters conducting water-bombing operations every day.