BANGKOK (Reuters) - Environment group Greenpeace on Thursday called on Thai Prime Minister Prayuth Chan-ocha to tackle an air pollution “crisis” in Bangkok, weeks after a pollution agency said the city’s air quality had hit dangerous levels.

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Air pollution has been under the spotlight in Bangkok, one of the world’s most popular tourist cities, with many residents complaining about smog.

Greenpeace said Bangkok suffered the worst air pollution in its history between Jan. 1 and Feb. 21.

The Pollution Control Department warned this month that the level of particulate matter smaller than 2.5 micrometres, or PM2.5 dust, in the city had hit unhealthy levels and asked children to stay indoors.

PM2.5 dust, the most dangerous kind, includes pollutants such as nitrates that can penetrate the cardiovascular system.

Critics blame Bangkok’s worsening air pollution on lax enforcement of vehicle emission standards, poor urban planning and insufficient green spaces.

Greenpeace activists presented an hourglass filled with dust from Bangkok and other provinces most affected by severe air pollution to a government representative.

“Bangkok cannot continue choking on hazardous air,” said Tara Buakamsri, director of Greenpeace in Thailand.

“It endangers the lives of people, affects economic productivity and negatively impacts the prestige of one of the most popular cities on earth.”

The prime minister, who is also the chairman of the National Environment board, should order an improvement in air quality, he said.

The PM2.5 level in central Bangkok was at 22.5 micrograms per m3 on Thursday, according to the AirVisual smartphone application.

Earlier this month, the pollution department measured PM2.5 dust in Bangkok at 72-95 micrograms per m3.

That compares with a World Health Organization (WHO) guideline of an annual average of no more than 10 micrograms.