SHENZHEN - When Mr Xie Yifa came to Shenzhen 26 years ago, it was a very different city.

Then, the Nantou village where he lived - one of several that dotted the nascent metropolis - was criss-crossed by dirt tracks, which would become a wet slurry when it rained.

Today, butcher and provision shop owners still hawk their wares along the narrow alleys, now paved with concrete. The city - once just fields, hills and saltpans interspersed with farming and fishing villages - today is a jungle of glass and concrete.

"So much has changed, you look around and there are skyscrapers everywhere," said 46-year-old Mr Xie, who works as a contractor.

Shenzhen was an experimental field for China's economic reforms which began in 1978. Then, Communist Party elders led by Deng Xiaoping launched China's reform and opening up policy with the goal of transforming the country's centrally-planned economy to one that was more market-driven.

Shenzhen was picked as one of four "special economic zones" along China's southern coast to pilot market-oriented policies - the others being Zhuhai and Shantou, also in Guangdong province, and Xiamen in nearby Fujian province.

Manufacturers, many of them from across the border in Hong Kong, were attracted by tax breaks and the mainland's plentiful labour.

In nearly four decades, Shenzhen transformed from a collection of rural villages of 300,000 people, to a megacity with an estimated population of 20 million, and a gross domestic product of 2.24 trillion yuan (S$442 billion), the third-highest for a city in China after Shanghai and Beijing.

City of migrants

Shenzhen's success has been hailed by Chinese state media, but its fortunes were built on the backs of ordinary Chinese - migrants from all over China such as Mr Xie, who took a chance and came seeking a better life.

This diverse fabric is made plain in the "urban villages" within the metropolis like the one Mr Xie lives in. In a single street there are shops selling noodles from the north-western city of Lanzhou, Chongqing hotpot, and smelly tofu from central Hunan province.

The city's lingua franca is not Cantonese like elsewhere in Guangdong province, but putonghua, or Mandarin.

Urban villages came about because while the city officials acquired farmlands for development, they left the farmers' residential land - their villages - alone. Farmers developed housing on these lands that they rented cheaply to migrant workers, providing much-needed affordable housing and other amenities to workers on low wages.

Mr Xie came to Shenzhen in 1992, the same year Deng completed his landmark "Southern Tour" of Wuchang, Shenzhen, Zhuhai and Shanghai, where he threw his weight behind the economic reforms, that changed Mr Xie's life.

Reforms had stalled in the aftermath of the 1989 June 4 Tiananmen incident in which hundreds - possibly thousands - died in the crackdown against pro-democracy demonstrations in Beijing. Deng's Southern Tour revitalised the reforms.

"Before this in the 1970s, it was very different, people lived and worked in collectives. But with the reform and opening, we had a choice to make a living for ourselves," said Mr Xie, who is from Ganzhou in Jiangxi province.

In Shenzhen, he worked a decade in a factory making plastic casings for electronics, and saved up enough money to set up his own renovation business, employing up to 10 workers each time he gets a project.

"How long will I stay here? I don't know, but I know in Shenzhen there will be opportunities, it just depends on whether you can grasp them," he said.

Millions of others thought so too, and crammed into the city, where they fuelled the economic boom.

The Hong Kong factor

Another factor responsible for Shenzhen's success is its proximity to Hong Kong, from which it drew ideas, capital and technology.

This was evident in Shekou, the first free-market industrial area set up in Shenzhen.

"When the Shekou Industrial Zone was being built, its way of management and the talents that ran the place were from Hong Kong," said Mr Brian Chen, who runs TAS, a social organisation that gives educational talks on Shekou's history.

The zone's founder, Communist Party cadre Yuan Geng, also learnt a thing or two about the free market when he was trying to get investors in Hong Kong to invest in the area.

"Shekou has a well-known slogan - Time is money, efficiency is life - the first part of the slogan is something Yuan Geng learnt dealing with investors in Hong Kong," said Mr Chen.

Professor Li Jinkui, senior research fellow at Shenzhen-based think-tank the China Development Institute, noted that in the days before economic reforms began, Shenzhen was still a farming society.

It was a far cry from Hong Kong which - ruled by the British as a colony from 1841 to 1997 - was an advanced industrialised society, with access to Western technology and capital.

He compared this difference to a "waterfall between civilisations" - once the doors were open, technologies and capital rushed in like water and, coupled with the plentiful labour on the mainland, powered the growth of Shenzhen.

"Of the four SEZs, Shenzhen is the closest to Hong Kong, this favourable position gave it a rare advantage," said Prof Li.

These factors led Shenzhen's GDP to grow a ferocious 22.6 per cent annually on average from 1979 to 2016, and last year grew 8.8 per cent, higher than the national growth rate of 6.9 per cent.

Price of progress

But the city's progress has also left some trying to catch up.

Madam Shen Xia, 38, who makes a living selling yellow wine in Nantou, says her rent has increased five-fold since she came to Shenzhen in 2001.

"The city is getting too expensive for migrants like me, if it keeps going up, I think I will have to go home," said Madam Shen, who is from Meizhou, another city in the same province.

Other migrants have also paid a price for helping build a city from nothing.

More than 600 workers from neighbouring Hunan province are petitioning the city's government for compensation.

They had developed silicosis, an incurable lung disease caused by prolonged inhalation of airborne silica dust, when working on construction projects in Shenzhen.

Even so, the city has not lost its attraction - it continues to pull in people from all over China, these days often professionals in its technology or financial sector.

"Most of the people here are originally from elsewhere, so Shenzhen is inclusive, it's a city of young people, not like Beijing or Shanghai," said computer systems engineer Chen Yongbin, 28, explaining why he came to Shenzhen from Jiangxi province five years ago.

Mr Chen, who has two children, has put down roots in Shenzhen and says he intends to stay here for the long haul.

Renowned poet Lu Xun compared hope to a path in the countryside - where once there was no path, after people begin to pass, a way appears.

For 40 years, millions have been drawn south to Shenzhen by the economic reforms that began there.

The city might have once been a muddy country road, but for the efforts of Mr Chen and the millions of others that came before him, it is now a wide boulevard.