Worsening haze across Indonesia, Singapore and Malaysia forces schools to close, airlines to cancel flights

* Haze forces school closings, flight cancellations in SE Asia

* State of emergency declared in two Indonesian provinces

* Police investigating 26 firms (Adds Indonesian minister's quotes)

By Michael Taylor and Kanupriya Kapoor

JAKARTA, Sept 15 (Reuters) - A worsening haze across northern Indonesia, neighbouring Singapore and parts of Malaysia on Tuesday forced some schools to close and airlines to delay flights, while Indonesia ordered a crackdown against lighting fires to clear forested land.

Southeast Asia has suffered for years from annual bouts of smog caused by slash-and-burn practices in Indonesia's Sumatra and Kalimantan islands, but governments in the region have failed to address the problem.

The fires have been exacerbated this year by the effects of the El Nino weather phenomenon, as a prolonged dry season in Indonesia has parched the top soil, fuelling the flames.

"The fire problems have reached a critical point," Luhut Pandjaitan, coordinating minister for political, legal and security affairs, told reporters.

"Our neighbouring countries have protested for years. We are not playing around."

President Joko Widodo, who was on an official visit to the Middle East, instructed security forces late Monday to accelerate efforts to extinguish the fires and revoke land permits from companies found responsible.

Nearly 3,000 military and police personnel, 17 helicopters and four cloud-seeding aircraft have been deployed to fight the fires, according to the country's disaster management agency.

A state of emergency has been declared in Indonesia's Riau and Central Kalimantan provinces as an air quality index has hit "dangerous" levels, rising to as high as 984, officials said.

In Singapore, the index has fluctuated well above 100, levels considered "unhealthy", for the past few days, and reached as high as 249 on Monday night, putting it in "very unhealthy" territory.

Indonesia has struggled for years to contain forest fires and the resulting haze despite repeatedly promising to punish perpetrators.

THOUSANDS SICK

The unhealthy air has caused acute respiratory infections for around 26,000 people in Indonesia's Riau province alone, a government official said.

It has also increased the workload for doctors in Malaysia and Singapore, where the haze has clouded the build-up to the Formula One night race later this week.

Malaysia said it was preparing to conduct cloud-seeding operations to reduce the haze as schools were closed in several states and some flights were disrupted due to poor visibility.

The smog is usually caused by firms and small-holder farmers clearing land adjacent to existing concessions for palm or pulp and paper.

Major plantation companies like Asia Pulp and Paper say they have a "zero burning" policy but have often been criticised by green groups for not doing enough to stop the haze.

Indonesian authorities plan to sanction this week three or four companies of the total 26 under investigation, said Environment Minister Siti Nurbaya Bakar, with the revoking of their land permits a possibility.

(Additional reporting by Bernadette Christina and Eveline Danubrata in JAKARTA, Trinna Leong in KUALA LUMPUR and Fathin Ungku in SINGAPORE; Editing by Randy Fabi and Simon Cameron-Moore)

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