Parts of Indonesia have been enveloped in the worst haze yet this year, officials said as residents donned face masks to ward off thick, choking fumes.

The haze, caused by forest and ground fires across Indonesia, descended on the province of South Kalimantan on Borneo island, reducing visibility and filling the air with noxious burning smells.

"We have had visibility problems because of the thick smoke since early in September, and today is one of the worst smoke attacks," said a spokesman for the South Kalimantan airport in Banjarmasin.

He said that no flights had been affected so far as the smoke had closed in after morning plane departures, but there had been 20 recorded disruptions to air traffic at the airport since September 1.

Officials blame fires set by large forest and plantation concession-holders, as well as by small farmers, to clear land for cultivation. The practice is illegal but officials find it difficult to enforce the law.

In 1997 and to a lesser extent in 1998, haze from forest fires in Indonesia enveloped parts of Southeast Asia for months, causing serious health problems and traffic hazards.

Trija of the meteorology station in South Kalimantan said that visibility was at 1.5 kilometres at midnight GMT, but had dropped to 3,000 metres one hour later and to 600 metres by 0300 GMT.

"There is no doubt that this is from burning activities. You can smell the burning and it is prickly to the eyes," said Trija. He said that face masks or wettened scarves or handkerchiefs were being worn people both outside and inside their houses.

Sumatra and Borneo islands – which border Singapore and Malaysia – are the areas usually hardest hit by the choking haze, an annual dry-season hazard in parts of Indonesia.