The National Environment Agency (NEA) said that slightly hazy conditions are expected to persist tonight. Pink Apple, an events company that organised the Garfield Run in Sentosa yesterday, shortened its races.

At 7pm, the 24-hour PSI stood at 75-88. But the three-hour PSI – an indicative reading – rose to 127, from below 70 in the morning.

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. This year’s strong El Nino has exacerbated the problem, creating extra dry conditions that fan the flames.

Widodo announced Wednesday that “firm legal action will be taken” against companies responsible.

Dr Erik Velasco, a research scientist from the Singapore-MIT Alliance for Research and Technology, confirmed that the typhoon that blew winds from the south-west – the direction of Sumatra, Indonesia – causing the haze to reach unhealthy levels earlier this week, has hit land.

Indonesia has for many years promised to step up enforcement of laws on illegal fires.

More than 100,000 people have been affected with acute respiratory infections in South Sumatra and South Kalimantan provinces.

Tens of thousands have fallen ill in parts of Indonesia as the haze thickened over the past fortnight, and the smog has led to unhealthy air quality and reduced visibility in neighbouring Singapore and Malaysia.

“My daughter keeps having to go to the doctor for her wheezing and blocked nose”, said C.S. Ebenezer, 46, a resident of Singapore, where many have been forced to wear face masks.

Last week, Malaysia had to close its schools in states like the capital Kuala Lumpur, Selangor and Malacca, affecting about 1.5 million students, reported The New Paper.

The haze problem has become a chronic threat to the world’s first night-time Formula One race as well as a festering bilateral issue with Indonesia, where fires have traditionally been used to clear land for cultivation.

“Those from the corporations include general managers and operational managers”.

He said the suspects would be charged with violating the Environment Law and Forestry Law, which carry a maximum 15-year imprisonment and a fine of about $700,000. “The president has ordered the military commander to deploy more soldiers to the affected areas”, he said.

There is still a huge gap between what has been agreed at the Asean level and what is happening on the ground in Indonesia for “people-centric” Asean to achieve its haze-free goal by 2020.

Indonesia, Singapore and Malaysia are choking under a thick haze of smog caused by the annual burning of land for the production of pulp, paper and palm oil on the island of Sumatra, in western Indonesia and Borneo.

Motorists commute along a road shrouded in haze in Kampar, Riau province on Sept.18, 2015.