3 Indian cities among the world's top 10 most polluted cities

Three Indian cities - Delhi, Kolkata, Mumbai- are among the top 10 most polluted cities in the world, according to IQAir, a Switzerland-based climate group that is also a technology partner of the United Nations Environmental Program.

While Delhi tops the list with an average air quality index of 556 as listed by the IQAir service, Kolkata ranks fourth with an air quality index of 177 and Mumbai sixth in the entire list with an AQI of 169.

Authorities on Friday advised Delhi residents to limit outdoor activities and told government and private offices to cut vehicle use by at least 30% as air quality in Delhi-NCR inched towards the emergency level amid a rise in emissions from farm fires and unfavourable meteorological conditions.

Also watch: Delhi: smog thickens, AQI worsens; residents asked to cut use of vehicles

Over 4,000 farm fires, accounting for 35% of Delhi's pollution on Friday, played a major role in pushing the 24-hour average Air Quality Index (AQI) to 471 by 4 pm, the worst this season so far.