Authorities urged people on Friday in the northern Thai city of Chiang Mai to stay indoors and work from home as air pollution levels spike. 

In recent weeks, smoke from forest fires and farmers burning crop stubble blanketed the popular tourist destination. 

The air monitoring website IQAir named Chiang Mai, on Friday morning, the most polluted large city in the world, surpassing usual hotspots such as Delhi and Lahore.

Levels of the most harmful PM2.5 particles, which are so small that they can enter the bloodstream, were more than 66 times higher than the World Health Organization's yearly guideline, according to IQAir.

Read next: Air pollution linked to increased dementia risk: Harvard report

Nirat Pongsittitavorn, governor of Chiang Mai province, released a statement asking people to stay indoors and work from home to "protect themselves and reduce the health impact" of PM2.5 particles.

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Thailand has been suffering from an increase in air pollution since the beginning of the year, which has been caused in part by seasonal agricultural burning.   

According to the public health ministry, nearly two million people have needed hospital treatment for respiratory conditions caused by air pollution this year.    

Only six countries meet WHO air quality guidelines

Officials previously warned Bangkok residents to stay indoors and work from home in February as the capital was covered with harmful haze.

A recent study revealed that only 13 countries and territories had "healthy" air quality last year, according to a new report, with alarming levels of air pollution surging in 2022.

The report by IQAir, a company that tracks air quality worldwide, found that 90% of the countries and territories which were analyzed exceeded the air quality guidelines set by the World Health Organization; the guideline was set to aid governments craft regulations and to protect public health.

Upon analyzing the average air quality from 131 countries and territories, IQAir found that only six countries and seven territories met the WHO air quality guidelines. The countries were found to be Australia, Estonia, Finland, Grenada, Iceland, and New Zealand. The territories in the Pacific and Caribbean included Guam and Puerto Rico.

Seven countries showed to have poor air quality that far exceeded WHO guidelines. The countries are Chad, Iraq, Pakistan, Bahrain, Bangladesh, Burkina Faso, Kuwait, and India.

The study focused on finding a particulate matter, PM2.5, the tiniest pollutant, yet the most dangerous. PM2.5 travels deep into lung tissues where it can enter the bloodstream when inhaled.