Pontianak – Indonesia's environment minister said on a visit to the smoke-choked island of Borneo on Friday corruption was blocking the international help needed to tackle forest fires.

The haze from the fires, often set by farmers and illegal loggers, has blanketed parts of the island for months, causing serious health problems and occasionally shutting schools and grounding aircraft.

Smoke from the fires is also affecting neighbouring Malaysia and Singapore, although it is not as bad as in 1997 and 1998, when dense haze cost regional economies $9 billion in damage to farming, transport and tourism.

"We are not able to handle this forest fire problem ... everybody knows that we need help," minister Nabiel Makarim told reporters in the West Kalimantan capital of Pontianak. "But low credibility in eliminating corrupt practices has hampered ... international institutions to help us on this annual haze and fire problems," he said.

Makarim's visit came as conditions deteriorated in the city of Palangkaraya – in the neighbouring province of Central Kalimantan – where visibility had fallen to below 50 metres.

"The haze has worsened today because light rain in some areas last night has raised the humidity," said Hidayat, an official at the Palangkaraya meteorology office told Reuters. "The possibility of more rain falling in the coming days is there ... but a full day of rain of more than 100 mm will be needed to put out the fire," he said.

Some schools in the city which reopened this week closed again on Friday and the main airport has been closed since the beginning of the month.

In West Kalimantan, where Makarim met officials to discuss ways to put out the fires, the pollution index reached 405, a level health officials consider dangerous.

Makarim said he was due to meet Malaysian Science, Technology and Environment Minister Law Hieng Ding in Kuala Lumpur on October 7 to discuss the problem.

Conservationists have long criticised Jakarta for failing to protect its natural resources and put a stop to slash and burn practices and illegal logging. Indonesia has said that its laws are too weak to deal with the problem but has promised to make reforms.