Ujjwal is a 22-year-old labourer sitting outside a makeshift tent in a posh part of New Delhi. By day he works on repaving the road. By night he sleeps on the pavement.

Like millions of Indians, he has migrated to the big city to find work and earn money. It is the only way he can gain any benefit from the mainly-urban economic boom which has swept through this country.

"There are so many more opportunities available here than there are at home," he says.

"You have to work hard and the hours are long. But I don't want to go back to my village in Bengal. I want to stay here in Delhi."

Hundreds of thousands of migrant construction workers live in Delhi alone, many of them working on big marquee projects in advance of next year's Commonwealth Games.

Ujjwal earns about 5,000 rupees ($102) per month and manages to send at least 1,000 rupees home to his family.

'Creaking'

But as more and more migrants arrive in Delhi, the pressure on land, on water supplies, and on urban infrastructure intensifies.

India's capital is creaking at the seams.

It's the same story across the developing world. Mega-cities have been growing at an incredible rate, and are struggling to cope with the demands of millions of new inhabitants.

Take the example of Mumbai. Its population has roughly doubled in the past 25 years, and millions of people live in the slums.

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