Jakarta (ANTARA News) - Haze from illegal land-clearing fires raging in Indonesia has closed schools, increased the number of people with respiratory ailments and disrupted air traffic, officials said Wednesday.

Schools in Palangkaraya, the capital of Central Kalimantan on the Indonesian part of Borneo, were closed Tuesday and Wednesday due to the dense smoke, an official from the provincial environmental impact management agency said.

"Education authorities may extend it (the closure) till tomorrow (Thursday) if the haze remains at dangerous levels," the official who identified herself as Anne told AFP.

Jono Kusanto, a doctor with the Central Kalimantan health office, said that local authorities and non-governmental organisations had been distributing face masks with priority given to health centres.

"It is already bad enough to breath at home, but in the open, it hurts even more," Kusanto told AFP.

He said the number of patients suffering from respiratory ailments "has certainly risen drastically since about two weeks ago". He could not immediately provide the latest figures.

Meanwhile at least two early flights to Palangkaraya's airport were delayed Wednesday when visibility was just 400 to 500 metres (yards), officials said.

Two further flight arrivals were also delayed for hours in Pontianak, West Kalimantan, where visibility of about 100 metres later improved to 1,000 metres, they said.

The latest satellite images dating from Tuesday afternoon showed 696 hotspots, or areas of high temperatures indicating fires, dotted across the Indonesian portion of Borneo.

On the nearby island of Sumatra island, where 336 hotspots were burning according to satellite imaging, fires were centered on inland districts, leaving the South Sumatra capital of Palembang only slightly affected, a local meteorology official said.

Indonesia's annual burn-off, which is outlawed but poorly enforced, causes a haze that typically smothers parts of Malaysia, Singapore and Thailand as well as Indonesia itself.

The grey haze enveloped Singapore on Tuesday and has been affecting air quality in Malaysia for several weeks.