Forest fires on Sumatra and Borneo are sending a toxic haze across the skies of Southeast Asia, raising air pollution levels on the two islands and in neighboring Malaysia, Singapore and Brunei.

Malaysia's Meteorological Services Department on Tuesday said a smoky haze was blanketing skies in the central Selangor state and the eastern state of Sarawak on Malaysia's part of Borneo island, causing air pollutant indexes at five stations to record unhealthy air quality levels.

The indexes, which measure harmful particles in the air, recorded moderate air quality levels in 38 other areas.

In Singapore, the pollutant standards index (PSI) dropped from "healthy" to "moderate" with a reading of 52. A reading of more than 100 is considered dangerous to the health, while 50 or below is good.

The haze from the fires also has affected Brunei, which experienced higher than normal air pollution levels Monday and reduced visibility levels of 5,000 meters.

Malaysia's Sarawak Deputy Chief Minister Tan Sri Dr George Chan warned the haze in the state was expected to worsen.

He said the Meteorological Services Department had forecast "less than normal" rainfall in Borneo until the end of the year, which would give rise to more brushfires and more haze.

The Jakarta-based ASEAN Secretariat said satellite images showed there were more than 350 "hot spots" detected in Riau, North Sumatra, South Sumatra, Bengkulu and Jambi, producing a haze that traveled throughout the region. It also showed more than 170 hot spots in Borneo, but did not state whether these fires were sending smoke across the region.

"Most of the fires have occurred in abandoned plantation areas and peat lands," according to a report issued by the secretariat Tuesday.

Triwibowo, the director for forest fire control at Indonesia's Forestry Ministry, confirmed the secretariat's report that most of the fires were on privately owned land. He said this was one reason it was so difficult for the government to extinguish the blazes.

"We deployed dozens of officers to put out the fires 10 days ago but they have been unable to deal with them," he told The Jakarta Post.

Triwibowo said his office was formulating new strategies for fighting the fires, including deploying helicopters and planes to drop water on the blazes.

"But that would still be difficult because the fires are scattered around thousands of hectares of land. I guess now is the time to pray for heavy rain."