The government has decided to take drastic measures to combat persistent haze caused by ultra-fine dust particles that have shrouded Bangkok and its vicinity, by deploying troops to check on factories and ordering the temporary closure of schools.

In a number of actions taken on Wednesday,  the Education Ministry ordered a two-day closure of state and private schools, as well as vocational education institutions, starting Thursday. Most students were sent home at noon on Wednesday.

"While universities are allowed to remain open, we will ask them to suspend classes," said Education Minister Teerakiat Jareonsettasin.

That said, some major universities -- including Chulalongkorn and Thammasat universities -- have suspended all scheduled classes until tomorrow.

Despite the closures, Dr Teerakiat said the Ordinary National Education Test (O-Net) for Prathom 6 and Mathayom 3 -- which is scheduled over the weekend -- will not be deferred.

"The Education Ministry will decide on whether or not the closures will be extended to next week," said Dr Teerakiat. "We are monitoring the situation daily."

Bangkok governor Aswin Kwanmuang ordered the closure of 437 schools run by the Bangkok Metropolitan Administration (BMA) until tomorrow.

"The decision was made to safeguard small children from health risks," Pol Gen Aswin posted on his Facebook page.

The governor said 50 drones will be deployed to spray water in critically haze-hit areas today and tomorrow, he said, adding City Hall is prepared to send mobile medical units for those affected by the haze over the weekend.

Meanwhile, deputy Bangkok governor Taweesak Lertprapan said that tomorrow, City Hall will invite construction firms -- including those working on state projects -- to talk about possible measures to reduce the amount of dust coming from construction sites.

"More stringent measures will be rolled out next week," he said.

Prime Minister Prayut Chan-o-cha instructed the Internal Security Operations Command (Isoc) to deploy soldiers in provinces to inspect emissions from factories.

"Soldiers will be checking factories to find out which ones are illegally discharging waste water, rubbish and toxic substances," said Gen Prayut, before vowing that vehicles and public buses which emit black exhaust fumes will be impounded right away.

"If the problem persists, I will only allow vehicles to operate on odd or even numbered dates," he said.

"If that fails, diesel-powered vehicles will be banned from haze-hit areas."