Smog from fires raging on Indonesia's side of Borneo island has disrupted air traffic in neighbouring Malaysia's Sarawak state which is choking under unhealthy levels of haze.

The haze situation in peninsular Malaysia is also worsening, with five states facing Indonesia's Sumatra island now hit by unhealthy air quality.

"The helicopter service, a key mode of transport in Sarawak, has been stopped due to poor visibility," an official with the Department of Civil Aviation in Sarawak's capital Kuching told AFP.

Three scheduled flights operated by Malaysia Airlines and a unit of budget carrier AirAsia were also diverted on Wednesday due to poor visibility, he said.

Helicopters are required to have a minimum visibility of 1.5 kilometers (one mile) but visibility in most parts of the state is now less than one kilometer, the official said.

Air quality in Sarawak continued to remain unhealthy in most areas, with Air Pollutant Index readings of between 106 and 188. The index considers haze levels of 100-200 to be unhealthy.

"Hopefully by the end of the month, when the monsoon season kicks in, we will have rain and we will see the end of the haze," a meteorological services department official said.

In peninsular Malaysia, locations in five states including the tourist destination of Malacca posted unhealthy air quality between 101 and 116, up from two states on Wednesday.

Malaysia is hoping to post a sharp rise in tourist arrivals and earnings next year but top travel officials have warned that haze from the Indonesian forest fires could choke the industry.

The Malaysian and Indonesian governments have outlawed land clearing by fire but weak enforcement means the ban is largely ignored.