SINGAPORE - The haze has worsened on Thursday (Sept 10), with the three-hour Pollutants Standard Index (PSI) rising into the "very unhealthy" range, hitting 207 at 11pm. At midnight the reading was 211.

It is the worst haze since April last year when the index measuring air quality was tweaked. Last year, the highest three-hour PSI was 153 on Oct 6, while the highest 24-hour PSI was 125 on Oct 7.

The three-hour readings breached 100 at 2am on Thursday and have been going up since. The 24-hour PSI at 11pm on Thursday was 132 to 148. A reading of 101 to 200 means that air quality is unhealthy. A reading of 201 to 300 indicates that air quality is very unhealthy.

In its haze update at 5pm, the National Environment Agency (NEA) said that for the rest of Thursday, the hazy conditions are expected to persist. The 24-hour PSI for the next 24 hours is expected to be in the low to mid levels of the unhealthy range, and may further deteriorate if the winds are unfavourable. For Friday, the prevailing winds are forecast to blow from the south-southeast or south, and hazy conditions can still be expected, it said.

In response to media queries, the Elections Department (ELD) has advised voters who will be out to cast their votes on Polling Day on Friday to take guidance from the advisory issued by the NEA, should haze levels remain in the unhealthy range.

On Thursday, Environment and Water Resources Minister Vivian Balakrishnan conveyed Singapore’s deep concern over the deteriorating haze situation to Indonesian Minister of Environment and Forestry Siti Nurbaya Bakar, when the number of hotspots in Sumatra rose from 140 on Wednesday to 328. He called for urgent action to be undertaken, including stricter action against the perpetrators.

Both he and Defence Minister Ng Eng Hen repeated Singapore’s offer of help. The authorities here have put on standby aircraft and personnel to seed clouds and carry out aerial firefighting, and a fire-fighting assistance team. On Thursday, Indonesia sent more than 1,000 soldiers to Sumatra to aid fire-fighting efforts.

When PSI inches above 100, the authorities advise healthy people to reduce prolonged or strenuous outdoor activity.

The elderly, pregnant women and children should do as little of such activity as possible, while those suffering from chronic lung or heart disease should avoid engaging in these activities.

The Ministry of Health, on its website, advises people to drink plenty of water to stay well-hydrated.

The haze, an annual occurrence, is caused by farmers in Indonesia who burn forests to clear their land for agriculture. The act sends smoke haze wafting northward to Singapore and Malaysia.

At least eight flights were cancelled on Thursday at Sultan Thaha Airport in Jambi city in Sumatra, Indonesia, according to Contact Center Angkasa Pura II, the state-owned airport operator for Sumatra and parts of Java islands, Bloomberg reported.

The fires are exacerbated by the local dry season. Indonesian authorities warned last week that this year's haze will be worse than in previous years, the Bernama news agency reported, and could last through end-November.

The S-League football match between Albirex Niigata and Tampines Rovers at Jalan Besar Stadium was postponed due to the haze. EtonHouse, which runs 17 pre-schools, suspended outdoor activities once the PSI crossed 100. Several firms here have started implementing contingency plans.

Doctors also reported a spike of up to 20 per cent in patients with haze-related conditions, such as blocked noses and irritated skin.

Dr Michael Lee, deputy medical director of Raffles Medical Group, said: “We expect to see more patients in the coming weeks if the haze continues to worsen.”

For haze updates in Singapore, members of the public can go to the haze microsite at www.haze.gov.sg, follow NEA's Facebook and Twitter page, or download the myENV app.