The blazes in peat swamp forests on Indonesia's Sumatra island have sent massive plumes of smog across the sea to neighboring Singapore and Malaysia, both of which are growing impatient with Indonesia's response to the problem that occurs nearly every year.

Singapore is suffering its worst haze in history. Singapore's main index for air pollution hit a measurement of 401 at midday Friday, exceeding previous highs of 371 on Thursday and 321 on Wednesday, both of which were record readings. Those measurements were classified as "hazardous" and can aggravate respiratory ailments.

Plagued by the stifling smell of burning vegetation that crept even into homes and offices in this wealthy city-state, residents flocked to pharmacies to buy protective face masks after Singapore's Prime Minister Lee Hsien Loong urged people to remain indoors as much as possible.

"I don't know if it's just my imagination but even indoors, my throat is starting to feel weird," said business manager Tan Joa-Quim. "I want a mask but my company has a limited supply, which we prioritized for the older and less healthy staff, and a lot of shops have sold out."

The dirty, acrid haze has slashed visibility and shrouded many of Singapore's towering landmarks, forcing airports to take extra precautions, the military to reduce outdoor training and some fast food businesses to suspend delivery services.

Singapore's environment minister flew to Jakarta, Indonesia's capital, on Friday to discuss measures to tackle the forest fires that break out in Indonesia during midyear dry spells because of carelessly discarded cigarettes and illegal blazes set by plantations and farmers to clear land.

Indonesia's National Disaster Management Agency said Friday it plans to soon use two helicopters in a "water-bombing" operation to assist more than 100 firefighters on the ground who are struggling to put out blazes.

The agency added that planes would be sent over parts of Sumatra in the next few days in a "cloud-seeding" effort to try to chemically induce rain. Some airports in Sumatra have also closed because of poor visibility and pollution levels that exceeded Singapore's.

In neighboring Malaysia, officials closed nearly 600 schools Friday in southern districts near Singapore. Most of Malaysia, including the main city, Kuala Lumpur, was not as badly affected, though two southernmost towns recorded hazardous air quality.

Singapore's Environment Minister Vivian Balakrishnan urged Indonesia earlier this week to take "urgent and definitive action" to combat the pollution at its source. But some Indonesian officials suggested that Singaporean and Malaysian firms involved in Indonesian plantations might be responsible for several fires, with one Indonesian Cabinet minister saying Singapore "should not act like children, making all that noise."