The world's most polluted capital cities have been revealed - and Delhi has been exposed as the worst.

Residents in India's capital city were exposed to more than ten times the safe amount of air pollution on an average day, a study has shown.

Dhaka, in Bangladesh, ranked second-worst with ten times the safe limit while Kabul, in Afghanistan, ranked third, with six times the same limit.

Researchers have revealed the world's most polluted capital cities, with Delhi, in India, ranking the worst followed closely by Dhaka, in Bangladesh

Kabul, Afghanistan, came third on the list. The top of the rankings were dominated by Asian and Middle Eastern cities

Out of 62 cities that featured in the study, 47 of them were found to be breaching WHO safe guidelines for harmful particles known as PM2.5s

New Zealand's capital city of Wellington tied with Ottawa, Canada, as the least polluted, falling well under WHO guidelines for safe amounts of air pollution.

Stockholm, in Sweden, completed the bottom three.

The report was published by IQ AirVisual and Greenpeace which calculated the average amount of PM2.5 air pollution in each city over the course of 2018 using publicly available records updated in real time.

Researchers focused on the amount of PM2.5s because they are the smallest and most harmful type of airborne particles because they lodge deep in the lungs.

Of the capital cities they looked at, the analysts found that only nine out of 62 for which data was readily available came in under the WHO's target of 10 micrograms per cubic millimeter of air.

A further six fell within a 'good' limit, meaning air quality poses little or no risk.

But 47 capital cities were identified has having a 'moderate' or worse risk of people developing health problems, with six ranking in the 'unhealthy' category, meaning an 'increased likelihood of adverse effects and aggravation to the heart and lungs.'

Wellington, in New Zealand, was ranked joint-least polluted alongside Ottawa, Canada

Only nine cities featured in the table fell under WHO guidelines (right), while another four were found to be over the guide but within safe levels

The study's authors wrote that poor air quality 'is the greatest environmental risk to health today' and contributes to an estimated 7million premature deaths each year.

Broadening the study to 3,000 cities located all around the world, they found that the worst offenders were in India and China.

Gurugram, in northern India, was found to have the worst air of any city in the world, with Faisalabad in Pakistan in third and Hotan, China, in eighth.

In total, authors found that 64 per cent of world cities exceeded WHO guidelines, with 100 per cent of measured cities in the Middle East and Africa breaking the limit.

Meanwhile 99 per cent of cities in South Asia, 95 per cent of cities in Southeast Asia, and 89 per cent of cities in East Asia also exceeded this target

Yeb Sano, executive director of Greenpeace Southeast Asia, said: 'Air pollution steals our livelihoods and our futures, but we can change that.

'In addition to human lives lost, there’s an estimated global cost of $225billion in lost labour, and trillions in medical costs.'