KUALA LUMPUR/JAKARTA • Fires in Indonesia that spread a smoky haze over South-east Asia this year burned at least 1.6 million ha of mostly degraded land and carbon-rich peatlands, data from a respected research group showed yesterday.

South-east Asia has suffered for years from smoke caused by fires in Indonesia, raising health and environmental concerns, but this year's fires were the worst since 2015, when 2.6 million ha were burned.

Slash-and-burn clearing by some palm oil growers is often blamed for the fires, which can then spread rapidly, especially during dry weather.

The Indonesian fires have been blamed for increasing greenhouse gas emissions and deforestation that endanger wildlife.

The Jakarta-based Centre for International Forestry Research (Cifor) said its analysis of satellite imagery from the first 10 months of the year showed much of the fires was in lands cleared years ago.

"We found that 76 per cent of burning occurred on idle lands. Those lands were forests a few years ago, but cycles of repeated burns have converted them into unproductive degraded scrublands," Cifor scientists led by Dr David Gaveau said in a statement.

About 3 per cent of the fires occurred on oil palm plantations.

Peatlands accounted for 41 per cent of the total land burned, or 670,000ha, in Indonesia this year, the Cifor data showed.

The scientists estimated around 60,000ha of rainforests were burnt this year as of October.

The Jambi and West Kalimantan provinces, which are important habitats for tigers and orangutans, saw some of the highest number of fires, they said. Their 1.6 million ha estimate of burnt land is based on an analysis across seven provinces.

Indonesia's Environment and Forestry Ministry did not immediately respond to a request for comment on the Cifor data. But an official had said earlier this year that 857,756ha of land was burnt as of end-September.