The report further states that India is projected to add the highest number of people to its urban population by 2050, ahead of China.
The Indian capital is expected to retain the spot of the world's second most populous city through at least 2030, when its population is expected to rise swiftly to 36 million.
Tokyo topped UN's ranking of the most populous cities in 2014 with 38 million inhabitants and while its population is projected to decline, it will remain the world's largest city in 2030 with 37 million people.
Mumbai, which ranks sixth on the list of the world's most populous cities in 2014, is projected to become the fourth largest city in 2030, when its population would grow to 28 million from the current 21 million.
The report said that the largest urban growth will take place in India, China and Nigeria between 2014 and 2050, with the three countries accounting for 37 percent of the projected growth of the world's urban population.
By 2050, India is projected to add 404 million urban dwellers, China (292 million) and Nigeria (212 million).
India's current urban population is 410 million people and this will grow to 814 million by 2050.
India and China account for 30 percent of the world's urban population.