Indonesia and its Southeast Asian neighbors are regularly hit by thick smog from slash-and-burn clearance of land and forests for agriculture, such as palm oil, causing premature deaths, respiratory infections, and school and airport closures.

Air pollution this year has been the worst since the last major haze outbreak in 2015, which was linked to more than 100,000 premature deaths in Indonesia, Malaysia and Singapore, according to a Harvard University study.

"(Indonesia is) not yet at what we had at the height of the 2015 haze crisis - but it might get there," Tim Christophersen, who coordinates the U.N. Environment Programme's (UNEP) land and climate change work, told the Thomson Reuters Foundation.

"Maybe the fires this year can serve as a reminder it's not mission accomplished yet," said Nairobi-based Christophersen, voicing concern that Indonesia's fires were being largely overlooked while those in the Amazon have won global attention.

With an El Nino weather pattern causing an extended dry spell, Indonesia closed schools this week, as well as providing oxygen at health centers, with thousands suffering respiratory infections due to choking smoke.

After the 2015 crisis, which cost the country $16 billion as more than 500,000 people sought medical care because of the toxic fumes, Indonesia switched its focus from containing fires to preventing them.

It introduced a permanent moratorium on forest clearing, trained communities and farmers in fire prevention, and set up a Peatland Restoration Agency to restore 2 million hectares (5 million acres) of carbon-rich peatland damaged by fires.

The last three good years have been relatively haze-free, and President Joko "Jokowi" Widodo used his record on reducing forest fires to successfully campaign for re-election this year.

But more than 328,000 hectares of forests and peatlands have been burnt since January, according to Indonesia's disaster agency, forcing neighboring Malaysia to take emergency measures, including issuing half a million face masks.

"The current fires in Indonesia are a reminder that while Indonesia is on the right path, and has made ambitious commitments and policy changes, the implementation is still not fully in line with their objectives," said Christophersen.

"It would be good to increase the investment in early detection and early firefighting capacities to have the highest effect once there are fires," said Christophersen, who used to head UNEP's REDD+ program to curb deforestation emissions.

REUTERS