Authorities warned that pollution levels in Bangkok and surrounding provinces had hit unhealthy levels on Thursday, ordering government employees in the capital to work from home for the next two days and urging others to do the same.
Air pollution is caused by a combination of crop-related burning, industrial pollution and heavy traffic, and a smoky haze covered the Bangkok's skyline.
Swiss air quality tracking website IQAir said the level of fine inhalable particles in the city was 15 times higher than the recommended level by the World Health Organization (WHO), making it the world's 8th most polluted city on Thursday.
"It's getting worse because there's too much smoke haze," said motorcycle taxi driver Kornpong Poprakun, 57. "I feel itchy eyes because there's a lot of dust, and breathing isn't easy."
According to the Geo-Informatics and Space Technology Development Agency (Gistda), 62 out of 77 provinces were shrouded with unsafe levels of particulate matter 2.5 micrometres and less in diameter (PM2.5) on Thursday morning with the worst level at 187.3 microgrammes per cubic metre (µg/m³) of air in Bangkok.
The average level of PM2.5 in the capital was 75.2 µg/m³ over the past 24 hours.
The government's safe threshold for PM2.5 is 37.5 µg/m³, while the World Health Organization (WHO) guidelines recommend 25 µg/m³.
Gistda reported at 11 am on Thursday that 40 provinces experienced red (seriously harmful) levels of . They ranged from 79.4 to 187.3 µg/m³ of air over the past 24 hours. The safe threshold is at 37.5µg/m³.
A woman walks in thick smog in Klong Toey district, Bangkok, on Thursday morning. (Photo: Somchai Poomlard)
Following Bangkok, the provinces with the highest pollution levels were Samut Songkhram, Ratchaburi, Nonthaburi, Samut Sakhon, Phrae, Nakhon Pathom, Pathum Thani, Phetchaburi, Sing Buri, Saraburi, Chai Nat, Ang Thong, Uttaradit, Suphan Buri, Ayutthaya, and Samut Prakan.
Prime Minister Srettha Thavisin told reporters that crop burning was the main culprit behind the spike, but added that around quarter of the pollution was from vehicles, a factor "we can control".
Mr Srettha said the government should consider limiting vehicles powered by fossil fuels in the capital to limit pollution in the long term, adding that the country's electric vehicle (EV) policy was also key.
The Department of Health has issued a warning, anticipating a rise in air pollution in Greater Bangkok over the next few days due to stagnant air.
Thanu Wongjinda, secretary-general of the Basic Education Commission, said school directors are now allowed to close their schools in areas of red PM2.5 levels for up to a week and introduce online teaching to protect students.
On Wednesday, the Bangkok Metropolitan Administration (BMA) called on state agencies and private organisations to allow their staff to work from home Thursday and Friday.
In a bid to curb traffic pollution, Bangkok Governor Chadchart Sittipunt told staff at the Metropolitan Administration's agencies to work from home and said other employees should also do the same.
He said some areas of the city had high levels of pollution and authorities were ready to manage the situation.
The government has offered subsidies to farmers to prevent burning and packages for cheaper electric vehicles while lawmakers are considering a clean air act for transport, business and agriculture to reduce pollution on a wider scale.