It is time to go back to the drawing board - again - in Shenzhen. The city has grown spectacularly over the past 18 months, but its future looks more uncertain than at any time in its two decades of existence. Investment by foreign and domestic companies, a barometer of future growth, is slowing sharply. This is not welcome news for the mainland's richest city, which has been a pioneer of economic reforms since Deng Xiaoping blessed it in 1980. Yet it can hardly be called unexpected. The city's cost of land and labour has been rising steadily for years, forcing manufacturing plants further away from the border between Hong Kong and Guangdong. Its vaunted hi-tech park, meanwhile, has been gradually giving ground to Shanghai. Even flagship firms like ZTE and Huawei now have research and design centres at the mouth of the Yangtze River. Shenzhen can do without sympathy, however. It simply needs its shackles to be loosened. No other mainland city has Shenzhen's youthful energy and passion for innovation. This should be channelled once more into a search for new solutions to its challenges - challenges that every other mainland city must eventually face in its economic development. Shenzhen already has a lot going for it, of course, which should kick in over the longer term. It is growing more enmeshed with Hong Kong every day. Cross-border traffic is booming and is set to further accelerate with the completion of a few major infrastructure projects over the coming years. Think about this: once the Western Crossing is finished late next year, it will be easier for New Territories' residents to fly out of Baoan International Airport than Chek Lap Kok (it is already cheaper). A shuttle bus from Central to Mission Hills Golf Club will take just over an hour. By the end of the year, the new Shenzhen MTR's first line will mean that Hong Kong visitors can walk through Lowu immigration and then get on a train that speeds across the Lowu, Futian and Nanshan districts within 30 minutes. There may still be passport controls between the special economic zone and the special administrative region, but they matter less and less. Nearly eight million people crossed their shared border last month. Yet for all this, Shenzhen officials still talk about the need to secure more land for the city to grow into, and about plans for massive projects to develop heavy industries. What they should instead be talking about more is the need to protect their natural resources for tourism, and focus their energies on plans to nurture a service economy. It is hard to achieve either of these aims, however, in the shadow of Hong Kong and Guangzhou's ambitions. The provincial capital obviously wants no competition for its heavy industries, while Hong Kong shrinks at the thought of service jobs moving across the border. What Shenzhen could really do with, therefore, is a bit of attention from Beijing. It remains the best place on the mainland to launch experimental reforms across a range of sectors. Easing licensing requirements for foreign professionals, for instance, could be tested there. And investment restrictions in sensitive industries could be lifted in stages. This would be a boon to the city, while limiting the risk for the rest of the mainland. Who knows, perhaps the biggest change of all could be handled most successfully in Shenzhen: real, genuine administrative reform. If Shenzhen is to continue to be a model of modernisation for the rest of the mainland, it needs to start building a modern system of government, one that functions more like Hong Kong's - or at least like Hong Kong's ought to. Anthony Lawrance is the Post's special projects editor