By Bernadette Christina Munthe and Glenys Kirana
JAKARTA (Reuters) - Indonesia's disaster agency urged prompt action against slash-and-burn plantation fires on Friday as the annual smoke "haze" begins to drift across the Malacca Strait to neighboring Malaysia and Singapore.
Fires in Indonesia, set in the dry season by companies clearing land for plantations, cause an annual crisis that at times blankets large parts of the region in choking smog, closing airports and schools and prompting warnings to residents to stay indoors.
Home to the world's third-largest area of tropical forests, Indonesia has been criticized by green activists and by neighboring Southeast Asian nations for failing to stop the annual fires.
"Smoke from forest and land fires in Riau has started to enter the Malacca Strait. Let's prevent and put out the fires," agency spokesman Sutopo Nugroho said on his Twitter account @Sutopo_BNPB on Friday, referring to a district on the main island of Sumatra.
He said that over the past week, the numbers of fire "hotspots" in West Kalimantan, on the nearby island of Borneo, had "increased significantly."
Dry weather that complicates firefighting efforts would reach its peak in September, Nugroho told Reuters, noting that the "critical period" for fires was from August to October.
The government's early announcement of a state of emergency for fires in five provinces this year had helped to prevent them from spreading as extensively as in 2015, he said, when El Nino made the problem worse.
"Countermeasures, including the response from the National Disaster Mitigation Agency, have been faster and better. Last year the emergency status was declared only after the fires were widespread," he said.
Heavy smoke from slash-and-burn clearing often comes from the islands of Sumatra and Kalimantan, where large forest concessions are used by pulp and paper and palm oil companies, some of which are listed in Singapore.
Singapore has pushed Indonesia for information on companies suspected of causing cross-border pollution.
"As we go through the legal process, all the information will be publicly available," Foreign Ministry spokesman Arrmanatha Nasir said on Thursday.
Indonesia imposed record fines against a local plantation company last week in the hope of deterring companies and individuals from using fire to clear land.
(Writing by Fergus Jensen; Editing by Nick Macfie)