Toxic smog has blanketed Vietnam's capital for more than a week, blotting out the skyline and leaving residents wheezing as Hanoi's air quality dipped to among the world's worst on Thursday.

The city of nine million ranked second only to India's New Delhi on IQAir's ranking of most polluted cities on Thursday morning, improving slightly in the afternoon.

According to the Swiss monitoring company, levels of PM2.5 pollutants -- cancer-causing microparticles small enough to enter the bloodstream through the lungs -- were vastly higher than the World Health Organization's recommended daily exposure limit.

"I have experienced difficulty in breathing out on the streets these days," resident Dang Thuy told AFP on Thursday, adding she had bought two new air purifiers for her apartment.

Hanoi a

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