Thick haze forced flights to be delayed, diverted or cancelled altogether at several airports in places such as Jambi and Palembang in Sumatra and Palangkaraya in Kalimantan yesterday, as visibility levels dropped below the 1km threshold for safe landings.
Officials in some affected provinces discussed measures including school closures if conditions worsen and the Pollutant Standards Index (PSI) exceeds 200.
In Kandis, Riau province, the PSI hit 435, as the haze reached as far north-west as Banda Aceh and Medan, some 600km away.
But the worst-affected areas were in Kalimantan, where health officials distributed masks and warned residents to stay indoors. Winds travelling westwards from Kalimantan drove the haze to Singapore over the past two days.
Indonesia's national disaster mitigation agency (BNPB) carried out cloud-seeding operations over Central Kalimantan in the past two days, using an air force Hercules aircraft, a spokesman said. The plane had been under maintenance earlier this week, when fires were at their peak.
Nine helicopters were also deployed across several provinces to conduct water-bombing operations to put out fires.
BNPB chief Syamsul Maarif has ordered more intensive cloud seeding and water bombing, especially as fires and the haze may pick up until next month amid drier weather.
Singapore's Environment and Water Resources Minister Vivian Balakrishnan wrote to his Indonesian counterpart Balthasar Kambuaya on Thursday to express concern over the haze and reiterate Singapore's offer of assistance to Indonesia to deal with the fires (see box below).
But Jakarta has previously said it would marshal its own resources to put out the fires, and yesterday, BNPB said: "We hope all national resources can collaborate to help regional governments put out forest and plantation fires in Sumatra and Kalimantan."
Meteorologists had some good news for the weekend. Said weather forecaster Dina Ike in Pontianak, West Kalimantan: "There is possible light to moderate rain in the next three days. The rainy season should start in mid-October at the latest."
Environmental activists continued to criticise the government for not doing enough to prevent the fires, an annual occurrence mostly caused by open burning, which is the cheapest way to clear land - but illegal.
"The government is not serious in tackling this," said activist Mukri Priatna from environmental group Walhi. "Getting the culprits is as easy as matching the coordinates of the hot spots with the concession coordinates of plantation companies. It doesn't do this."
But the World Resources Institute was more optimistic, saying in a note yesterday that the Indonesian Parliament's vote to ratify an Asean haze agreement could put more pressure on officials to enforce the country's laws.
It noted that there was greater momentum to crack down on illegal burning, saying: "Recent events show that Indonesia is taking the fires more seriously."