JAKARTA - Air quality in Riau's capital of Pekanbaru worsened to a record low on Sunday (Sept 22) after the haze intensified as a result of raging fires in the province, but especially in neighbouring Jambi and South Sumatra provinces.

The PM10 Pollutant Standards Index (PSI) in Pekanbaru surged at 10pm to cross 700, above the levels seen during Indonesia's worst haze episode in 2015.

The reading dropped to 489 at 7am on Monday.

Riau province has been blanketed in thick haze originating from neighbouring provinces Jambi and South Sumatra. The three provinces are among the closest to Singapore.

Riau, the Indonesian province second closest to Singapore after the Riau Islands province, was forced to shut schools for a week due to acrid haze that has seen the air quality hover between unhealthy and hazardous levels.

"The winds blew the haze from Kalimantan, South Sumatra and Jambi towards Riau," Dr Agus Wibowo, acting spokesman of Indonesia's disaster management agency (BNPB) told The Straits Times. "Meanwhile Riau itself is also producing haze."

Pekanbaru had registered a record PSI of above 600 during the haze crisis of 2015.

Reaching a peak in October, the haze that year had its epicentre in Central Kalimantan and was fuelled by severe drought. It sent air pollution indices soaring to record levels across large parts of Kalimantan, Sumatra, Singapore and Malaysia.

Indonesia has suffered haze episodes in most years since 1997 due to the fires mostly caused by farmers and companies clearing land using illegal slash-and-burn techniques to save costs.

A number of morning flights to Pekanbaru's Sultan Syarif Kasim II international airport were diverted or cancelled, Mr Yohanes Harry Douglas, spokesman for government air-traffic control agency Airnav, told The Straits Times.

Flights resumed normal operations in the afternoon after visibility improved, although it still remained below the required 1,000m, the usual minimum visibility level for any plane to land.

Several airlines, including Garuda Indonesia, Lion Air and Wings Air, opted to go ahead with flights at visibility of around 600m, Ms Safitri, a customer service officer at the airport, told ST.

Riau schools will remain shut this week.

Last Friday, firefighters battled raging fires at two locations in Pekanbaru, set just a few days after Indonesian President Joko Widodo visited the area to see for himself the fires that the authorities believe were started intentionally to clear land for plantation and other commercial purposes.

One of the conflagrations being fought last Friday in the heart of Pekanbaru was in an area measuring some 15ha - roughly the size of 10 football fields - in Bukit Raya, near the airport.

The Bukit Raya fire was started intentionally, said Mr Burhan Gurning, head of the Pekanbaru firefighting department, describing how stones had been placed in some parts of the land, indicating a plan to sink foundations for buildings.

Another fire, covering about 5ha, was in Payung Sekaki in north Pekanbaru.

Both fires were near residential areas, unlike the others, which are burning mostly in remote forests.

Riau, in the central part of Sumatra, is seeing the peak of its dry season. Rain could fall only by the middle of next month, according to weather forecasters.

Meanwhile, several flights between Ipoh in Malaysia and Singapore were cancelled on Sunday morning because of poor visibility, Bernama news agency reported.

Six of 14 scheduled flights at Ipoh's Sultan Azlan Shah Airport had to be cancelled.

Airport manager Mohd Ali Osman said they included flight by AirAsia flying between Ipoh, Johor Baru and Singapore.

Scoot, Singapore's budget carrier, also had to cancel flights between Singapore and Ipoh. The cancellations affected 747 passengers.

Malaysia has been struggling to deal with the haze over the past weeks that it says is a result of fires in Indonesia. On Sunday, all the monitoring stations in Perak showed the air quality was unhealthy, said Bernama.

As at 8am, 38 areas in the country had unhealthy Air Pollution Index (API) readings, compared to 18 last Saturday, Bernama reported.

These locations were in Johor, Kedah, Melaka, Pahang and Terengganu.

In Kuala Lumpur, the API readings in Cheras and Batu Muda remained in the unhealthy category at 153 and 173, respectively, Bernama said, while Putrajaya recorded an API reading of 138.

In Sarawak, the air quality in Sri Aman hit the very unhealthy range at 12pm, with a reading of 202.

The Star also reported that 57 schools in Kuala Langat and Klang districts will be closed on Monday after API readings went over the 200 mark.

Some 68,000 students will be affected, said the Selangor Education Department.

In a separate statement, the Education Ministry said that all the 296 schools that were closed last Thursday and Friday in Kuala Lumpur will operate as usual on Monday after API readings in those areas showed improvements.