Singapore slammed "shocking" statements from Indonesian officials over the haze crisis as it closed all schools and distributed protective face masks Friday in emergency measures after the air pollution index soared to hazardous levels.

The city-state has been cloaked in smog blown in from tinder-dry Sumatra island for about three weeks, the worst such episode since mid-2013 in a crisis that grips the region nearly ever year during the burning-off season.

The closure of primary and secondary schools as well as government-run kindergartens due to the haze problem is unprecedented, the Straits Times daily said as the air quality index shot up above 300, a level considered "hazardous".

As the pollution index rose, so did tempers, with Singapore Foreign Minister K. Shanmugam speaking out against some Indonesian figures who made light of the problem which has long strained relations among affected countries including Malaysia.

While Jakarta says it is taking steps to deal with the problem, "at the same time, we are hearing some shocking statements made, at senior levels, from Indonesia, with a complete disregard for our people, and their own," the minister said in a Facebook post late Thursday.

"How is it possible for senior people in government to issue such statements, without any regard for their people, or ours, and without any embarrassment, or sense of responsibility?" he said.

Shanmugan did not identify the officials, but Indonesian Vice-President Jusuf Kalla has made waves in recent weeks by repeating comments he made in March that Indonesia's neighbours should be grateful for good air quality most of the year.


'Never thanked us'

"For 11 months, they enjoyed nice air from Indonesia and they never thanked us," he said at the time.

Indonesian presidential spokesman Ari Dwipayana declined to comment on Shanmugam's remarks, but said Indonesia's neighbours should also take note of Jakarta's efforts to contain the fires.

"The president has stated that all force has been mobilised, we are going all out to put out the fires by water-bombing and weather modification," he told AFP.

"The president has also directly visited the impacted area, and this shows how serious we are in handling the forest fires and haze," he said, referring to Indonesian leader Joko Widodo's trip to smog-choked areas on the Indonesian part of Borneo island.

Singapore's Prime Minister Lee Hsien Loong said that offices will remain open Friday but that face masks will be distributed at community centres across the island for needy and elderly citizens.

The haze conditions improved somewhat throughout the day, below the level considered hazardous and into the high end of the "very unhealthy" range.

Lee said that Singapore has offered Indonesia help in putting out the fires "and asked them to share with us the identity of companies responsible for causing the haze".

Indonesia has previously said that Singapore-based companies were among those responsible for the blazes, caused by smallholders and agricultural companies using burning as a method to clear land for plantations during summer.

Under pressure from its neighbours to stop the annual haze, Widodo has pledged to crack down on companies and individuals behind the burnings.

About 3,000 troops and police have been sent to Sumatra to fight the fires, with Indonesian authorities saying last week it would take a month to bring them under control.

Indonesian environment ministry spokesman Eka W. Sugiri, said a total 25 air aircraft have been deployed to fight the fires through water-bombing and chemically inducing rainfall.