Air pollution in Singapore soared to record heights for a third consecutive day, and Indonesia prepared planes and helicopters to battle raging fires blamed for hazardous levels of smog in three countries.
Singapore's main index for air pollution hit a measurement of 401 at midday yesterday.
That exceeded previous highs of 371 on Thursday and 321 on Wednesday, both of which were record readings. Those measurements were classified as "hazardous" and could aggravate respiratory ailments.
Indonesia's National Disaster Management Agency said it plans to use two helicopters in a "water-bombing" operation to assist more than 100 firefighters on the ground.
Indonesia also deployed helicopters to artificially create rain.
At an emergency late-night meeting, President Susilo Bambang Yudhoyono ordered disaster officials to "immediately mobilise all the country's resources" to extinguish the fires on Sumatra island that have created vast palls of smoke.
Indonesia's disaster agency said two helicopters with cloud-seeding equipment were sent early yesterday from Jakarta and Borneo island to Riau province, where hundreds of hectares of carbon-rich peatland are ablaze.
"Hopefully, we will be able to create artificial rain today," said agency spokesman Sutopo Purwo Nugroho.
Firefighters tackling blazes in Bengkalis district, the worst hit area, were "overwhelmed" and unable to cope, said Ahmad Saerozi, head of the conservation agency in Riau province.
"We have been fighting fires 24 hours a day for two weeks," he said, adding that aircraft must drop water as soon as possible. "We can't do this alone," he said.
Singaporean Prime Minister Lee Hsien Loong said on Thursday he expressed "serious concern" in a letter to Yudhoyono and requested evidence that Singaporean or Malaysian companies were responsible for the "illegal burning", as suggested by some Indonesian officials.
Disputes between the two neighbours flare up regularly over haze. The Malay Peninsula has been plagued for decades by forest fires in Sumatra to the west and Kalimantan on Borneo island to the east.
"Singapore should not be behaving like a child and making all this noise," Agung Laksono, the minister co-ordinating Indonesia's response to the haze, said on Thursday.
Officials had detected 60 hot spots in Riau, Nugroho said, down from 148 two days ago, with 80 per cent of those in plantations and 20 per cent in forests. Singapore has provided satellite data to help identify the companies responsible for the fires.
Malaysian Deputy Natural Resources and Environment Minister James Dawos Mamit said his country was willing to send firefighters.
"If they need our help, we will offer whatever assistance we can," Dawos said.
Lower visibility from the smog has prompted Singapore's Changi Airport to increase the time between take-offs and landings, the aviation authority said.
The Singapore Flyer, which operates the city state's ferris wheel, suspended operations yesterday.
And the Singapore Shipping Association warned yesterday that the smog could lead to accidents in the busy Malacca and Singapore straits, risking a potentially devastating oil spill.
In Malaysia, officials closed nearly 600 schools in southern districts near Singapore. Most of Malaysia, including Kuala Lumpur, was not as badly affected, though two southernmost towns recorded hazardous air quality.
Bloomberg, Agence France-Presse, Associated Press