BANGKOK: The Thai government has ordered a crackdown on farmers flouting a ban on crop burning, as pollution in Bangkok spiked on Friday a week after toxic air forced hundreds of schools to close.

Smoke from farmers burning crop stubble combines with vehicle and factory emissions to send air pollution in Bangkok and other cities soaring in the early months of the year.

On Friday morning, the sprawling Thai capital was seventh on the list of the world`s most polluted cities run by air monitoring company IQAir.

The level of PM2.5 pollutants cancercausing micro particles small enough to enter the bloodstream through the lungs hit 86 micrograms per cubic metre,according to IQAir.

A reading above 15 in a 24-hour period is considered unhealthy by the World Health Organisation.

The Thai government ordered provincial authorities on Thursday to enforce a ban on burning crop stubble, requiring them to report how many farmers they have arrested for breaching the rule.

`In every province, if you allow crop burning or fail to implement preventive measures, you will be punished,` the government said in a statement.

More than 1.1 million pollution-protection masks have been distributed around the kingdom, and the health ministry is to monitor vulnerable groups, including children and pregnant women.-AFP