By Nils Blythe
Business correspondent, BBC News, Chongqing, China
Drive from Chongqing airport towards the city centre and the first things you notice are the cranes.
Thousands of migrant workers arrive in Chongqing every week
A grim mixture of mist and man-made pollution usually makes it difficult to see very far in this sprawling metropolis on the banks of the Yangtse River.
But even in the gloom I count fifty huge construction sites before we are halfway to our hotel.
The population of the city is expected to grow by 40,000 people this month, and every month for years to come.
The municipality of Chongqing, which includes a chunk of surrounding countryside, already has a population of 31 million.
That is more than half the number of people who live in Britain.
And there seems almost no limit to Chongqing's ambition for future growth.
This is China's new economic frontier.
The country's extraordinary development began in the coastal cities, powered by a seemingly limitless supply of cheap labour.
But as costs and wages have risen in those areas, businesses are looking west for new, cheaper places to operate.
Chongqing lies more than a thousand miles inland.
And the city authorities - ever eager to attract new investment - claim that wage rates for many jobs here are half of those in some of the coastal cities.
But Chongqing still has no difficulty in attracting new migrants from the vast rural hinterland of China's south west.
Many come hoping to get work in a factory.
I was introduced to a young assembly worker, newly arrived from a tiny village.
His pay is £80 a month.
And although he admitted that he had found the transition to city life quite difficult, the money was far more than he could hope to earn at home.
Beast of burden
Less well educated migrants - or less lucky ones - may end up working as "bang bang men".
Mr Shan employs about 12,000 people in Chongqing
You see them everywhere in Chongqing, carrying everything from building materials to shop supplies or tourists' suitcases.
The "bang bang" is a stout pole, which is placed across the shoulders.
A load is attached by rope and carried up the city's steep lanes and alleys by the human beast of burden.
I was taken to a tiny flat crammed with bunk beds, home to more than 20 "bang bang" men, to hear about their working lives.
For example, how heavy are the loads?
Often more than a hundred kilos, a young man told me.
And what do you weigh yourself, I asked - 58 kilos, he told me.
After much conferring, they reckoned that typical earnings for a "bang bang man" were about £40 a month.
Most of them said that they were able to send money home to their families in the countryside.
And they were looking forward to Chinese New Year, on 18 February.
It is the only time when most of China's 150 million migrant workers get a chance to go back to their families in the rural areas.
But although the work looked back-breaking to me, the "bang bang men" I met were a cheerful lot.
And, incidentally, quite knowledgeable about English Premiership football.
(One of them told me that Arsenal's young star Cesc Fabregas was his favourite player.)
Perhaps the optimistic spirit of Chongqing was best summed up for me by Yin Ming Shan, the founder of the Lifan motorcycle and car-making business in the city's suburbs.
He was jailed in the early 1960s for holding politically "incorrect" views.
Then he survived Chairman Mao's Cultural Revolution, when to be even a little richer than your neighbours would lead to forcible "re-education" in the impoverished Chinese countryside.
Now in his late 60s, Yin Ming Shan employs about 12,000 people in Chongqing, many of them migrant workers from the countryside.
I ask him if he is proud of what he has achieved.
Yes, he says. But one day soon he would like to be employing 50,000 people.
That's a lot of people.
But this is the city where almost that number of new migrant workers arrive every single month.
Nils Blythe and Hugh Sykes will be reporting daily from China for the PM programme on BBC Radio 4 for two weeks, starting on Monday 5 February.