Indonesia has begun seeding clouds in an attempt to create rain to put out blazes that have choked Singapore and Malaysia with smog, officials said, while launching investigations into plantation firms suspected of starting the fires.
The pollution index dropped to moderate in Singapore yesterday after having hit hazardous levels but the smog intensified in Malaysia, with its government declaring a state of emergency in two southern districts.
An aircraft with cloud-seeding equipment managed to unleash rain over Bengkalis district on Sumatra island, where some of the biggest fires are raging, said Indonesian disaster management agency official Agus Wibowo.
Indonesian police said they were probing eight companies with possible Malaysian links that are suspected of starting the fires, a day after environment group Greenpeace said the blazes were on palm oil plantations owned by Indonesian, Malaysian and Singaporean firms.
In Indonesia's Riau province, police spokesman Hermansyah said: "They are suspected to be Malaysian.
"It's a very serious crime. Fire-starters can be jailed and companies can be sued. They usually do it at night in remote locations, making it difficult for us to trace them. But we will do our best to pin them down."
Wibowo said the pollution standards index in Riau, where the fires are burning, exceeded the hazardous 400 level in several areas. Three helicopters also dropped water to douse fires on hundreds of hectares of carbon-rich peatland that have engulfed neighbouring Singapore and Malaysia in smog.
Malaysian Environment Minister G. Palanivel said the air pollutant index (API) hit 750 in the town of Muar - a 16-year high - early yesterday, with two other towns also reaching hazardous levels.
"The prime minister has signed a declaration of emergency for Muar and Ledang districts," Palanivel said.
The highest ever API reading was 860 during the 1997-1998 haze crisis that gripped the region. Hundreds of schools have been closed since Thursday in Muar, which has a population of about 250,000.
Many Malaysians have begun wearing masks as a precaution as the pollution levels have climbed.
Malaysia's API indicated that the capital Kuala Lumpur was also experiencing unhealthy air which had limited visibility to just one kilometre, according to Palanivel.
The annual haze problem is blamed by Indonesia's neighbours for affecting tourism and public health. The haze hit its worst levels in 1997-1998, costing Southeast Asia an estimated US$9 billion from disruptions to air travel and other business activities.