Indonesia is stepping up efforts to fight spreading forest fires in Central Kalimantan province on Borneo Island that have moved closer to residential areas and public roads.
The dry season is expected to peak soon in the province, prompting the authorities to increase their fire-fighting efforts.
Two helicopters were deployed on Tuesday to Palangkaraya, the provincial capital, for water-bombings runs to remote areas.
"We have started water bombings in Central Kalimantan. The ground and air teams are ready in five provinces," Mr Dody Ruswandi, the secretary-general of Indonesian disaster mitigation agency, told The Straits Times.
Fires have also occurred in Sumatra and Java.
"The situation in Sumatra is under control," Mr Dody said.
Three areas in Central Kalimantan with forest and plantation fires are Palangkaraya, and the regencies of Pulang Pisau and Gunung Mas.
Other Indonesian areas vulnerable to fire are West Kalimantan province and three provinces in Sumatra: Riau, Jambi and South Sumatra. The haze from forest fires that affects Singapore is usually from Sumatra.
Haze pollution caused by these large fires from Kalimantan are unlikely to reach Singapore unless there is strong wind blowing towards Singapore from the area.
On Monday, each of the five provinces prone to fire received a deployment of about 1,500 military personnel and police officers to help with fire-fighting efforts, Mr Dody said.
The peak of the dry season is usually August and September in South and Central Kalimantan.
Fire-prone Riau province, the part of Indonesia closest to Singapore, has two dry seasons a year - February-March and June-August - and the wind direction in the latter season would be towards the north-east, or in the direction of Singapore and the Malaysian peninsula, according to Indonesian weather agency BMKG.
President Joko Widodo's administration has been resolute in tackling forest and plantation fires as well as illegal logging, following fires in 2015 which caused more than 500,000 Indonesians to suffer respiratory ailments after being exposed to the choking haze that travelled across borders and blanketed parts of Singapore and Malaysia.
Stepped-up law enforcement - including a shoot-on-sight order against fire-starters - and better fire-fighting equipment mandated for plantation firms have resulted in a significant decline in the scale of the fires, an annual phenomenon usually in the dry season.
Mr Joko has cracked the whip on local officials, too, issuing an unprecedented threat to sack any provincial police chief or local military commander in areas where fires spread uncontrollably.
But still, the spreading fires in Central Kalimantan this week came as Mr Joko lost a Supreme Court appeal in a case where a group of citizens filed a class-action suit accusing the President's administration of negligence that led to the 2015 fires.
Indonesia's highest court upheld an earlier ruling that parts of the government were negligent. The Supreme Court decision means the government has to step up fire-prevention measures.
The ruling, as requested in the citizens' class-action suit, orders the government to issue more restrictive regulations to prevent fire, draw up a road map on forest-fire mitigation and emergency response, give compensation to victims as well as review concessions given to recalcitrant plantation companies.
Responding to the court's latest ruling, Ms Nur Hidayati, the national executive director of the Indonesian Forum for the Environment, said: "Every year, new generations of Indonesians are exposed to fires and haze while palm and pulp companies benefit from poorly enforced laws and a lack of transparency, allowing them to continue clearing forests and draining peatlands."