On the outskirts of Changsha in southern China stands a new tower. Its size is modest by Chinese standards.

At a mere 204m it's less than a third of the height of Shanghai's tallest. Its blocky glass and steel form may be unlikely to win any architectural beauty awards.

But what is startling is the speed at which it was built. A time-lapse video shows it shoot up at the rate of three storeys per day.

For the man behind it, Zhang Yue, this is only the beginning.

“Humans have experienced revolutions in industry, agriculture, transportation and information, but not yet in buildings,” says the handbook of the company he founded, Broad Group.

 Here now comes the revolution.”

The revolution will be modular, Zhang insists. Mini Sky City was assembled from thousands of factory-made steel modules, slotted together like Meccano.

It's a method he says is not only fast, but also safe and cheap.

Now he wants to drop the “Mini” and use the same technique to build the world’s tallest skyscraper, Sky City.

While the current record holder, the 828m-high Burj Khalifa in Dubai, took five years to “top out”, Zhang says his proposed 220-storey “vertical city” will take only seven months - four for the foundations, and three for the tower itself.

And it will be 10m taller.

But if that was not enough, Zhang Yue wants nothing less than to reimagine the whole urban environment.

He has a vision of a future where his company makes a third of the world's buildings – all modular, all steel, and all green.

“The biggest problem we face in the world right now isn't terrorism or world war. It's climate change,” he says.