A multinational effort to fight forest fires in Indonesia began on Sunday (Oct 11) as Singapore joined forces with other countries to help douse fires in South Sumatra.

A Chinook helicopter from Singapore was sent to Indonesia at the weekend to help in firefighting operations there, one of Indonesia's worst-hit areas.

The Chinook, which had a 5,000-litre water bucket, worked with a Bombardier water bomber from Malaysia, which can scoop 6,000 litres of seawater.

They joined two air-tractor water bombers from Indonesia's Environment and Forestry Ministry and six choppers from its Disaster Management Agency (BNPB).

Indonesia accepted Singapore's help last week after turning down its earlier offers.

In a statement to the media on Sunday, BNPB spokesman Sutopo Purwo Nugroho said Australia's L-100 Hercules aircraft will arrive by Wednesday. "This aircraft will operate for five days in South Sumatra as it will be needed to fight fires in New South Wales," he said.

Indonesia is waiting for more aircraft from other countries to help douse the fires, Dr Sutopo said.

Russia is expected to send a Beriev Be-200 aircraft, which can scoop 12,000 litres of water from a lake or the sea; China is also expected to send a few aircraft.

On Facebook on Sunday, Singapore's Defence Minister Ng Eng Hen said conditions for the water-bombing operations in Palembang, South Sumatra, were difficult as thick smoke affected visibility.

Meanwhile, visibility across Singapore was generally good yesterday, with the 24-hour Pollutant Standards Index (PSI) in the range of 84 to 93 at 10pm. At 10pm, the three-hour PSI was 111.

In its advisory on Sunday, the National Environment Agency (NEA) said the 24-hour PSI for the next 24 hours is expected to be in the moderate range, and may enter the low end of the unhealthy range if denser haze is blown in from the surrounding region.

The NEA said 129 hot spots were detected in Sumatra on Sunday. Prevailing winds are forecast to be weak on Monday, and occasional slight haze can be expected, with visibility likely to be in the normal range.