On the left-hand wall of Xu Liang's trading booth are a selection of framed verses from the Koran and an oil painting of Mecca. On the opposite side hangs a neon back-lit image of Vishnu, teasingly adjacent to three different sizes of crucifix (M, L, XL) and a portrait of Buddha looking admirably serene about it all.

As a Romanian customer enters, Ms Liang beams widely, rising from her chair to reveal the cluttered back wall and the majestic horror of Da Vinci's Last Supper in clumsy, primary-coloured tapestry. These little beauties, she says, are selling incredibly well in Italy.

Few places so monstrously and precisely define China's commercial ambition as Yiwu, a city 120 miles south of Shanghai. Ms Liang, along with the other 30,000-or-so wholesalers peddling alongside her in the sprawling enormity of the International Small Commodities Market, is not interested in whether the Romanian is offended or charmed by her multifaith cavalcade of tackiness. Her mission, pursued year-round from the same three metre-by-five metre booth, is to extract orders for hundreds or thousands of Last Suppers, so that the factory 30 miles away can get on with churning them out and freighting them west.

Other storeholders pursue a similar goal for more or less every product imaginable, from vacuum cleaners, Christmas decorations, knock-off iPods and shirt buttons to bidets, Wellington boots, LCD televisions and shaving foam. It is the goods' destination that is most significant: not Wal-Mart, Carrefour and Tesco, but the millions of small shops and traders in emerging markets whose aggregate buying-power is vast and growing.

Carefully ghettoised in Yiwu according to product type, hundreds of factory representatives in the complex play the same incongruous game as Ms Liang, shunting shoddy authenticity around the world with a “Made in China” sticker somewhere underneath. The guiding principle is not so much that the customer is always right, but that the customer is always everyone.

At present, the aisles of International Trade City are subdued. The faltering global recovery has kept crude oil and commodities far below their peak and the slump in European and American consumption is not helping. Grumbling booth-holders scoff at the idea that visiting buyer numbers are anything like the 50,000 per day claimed by officials. A third of that figure seems more plausible. Yet Yiwu remains the holy-of-holies for a devout mercantile faith: that the world cannot ever lose its appetite for cheap goods.

All of the stuff on show is cheap but, crucially, not all of it is nasty. The goods in Yiwu, say the buyers, are constantly improving. It is a difficult concept to grasp in a hangar full of knock-off Ninja Turtles and faux-satin Valentine's Day cushions, but, as China's trade tendrils stretch further, the quality of demand is rising in lock-step with quantity.

Plenty has been said about China's thickening ties with the developing world - the relentless trickle of mineral or energy contracts that extract nervous frowns from Washington, particularly when reciprocated with hefty loans from Beijing - but beneath those headline-grabbing deals, smaller, vastly more numerous links have been forged through the sort of small-scale commerce that starts in Yiwu and ends in a Brazilian night-market or a Yemeni souk. The sheer weight of this micro trade, particularly with the Middle East, may prove pivotal in China's quest for global influence.

Placed in its rightful global context, the Yiwu market, Ben Simpfendorfer, RBS's chief China economist, argues, stands at the eastern end of a New Silk Road, a nexus of trade links between China and the Middle East that may soon assume colossal geopolitical and economic importance.

And the growth of that importance can now be measured. Liang's daily pace of trade, in combination with hundreds of other Yiwu traders, feeds data into the “Yiwu Index”, a numerical reckoning of the flow of small goods leaving the world's biggest wholesale market and a kind of barium meal for tracking the rising scale and sophistication of the “Made in China” brand.

The past few weeks alone have told an interesting story: the main Yiwu Index, having lurched higher between 2007 and 2008 in line with high oil prices, fell sharply below its base-line earlier this year as the world trembled with economic terror. Over the past six weeks, with Beijing's stimulus package starting to work and the blood returning to the cheeks of emerging market consumers, the index has begun a tentative rise.

When the Yiwu Index does begin to advance more strongly again, its trajectory will describe China's global growth as Beijing would love to be known around the world: the neutral merchant in a partisan bazaar. The same principle applies to its flight path as a soaring geopolitical power. Yiwu, its customers and its astonishing array of goods bear far more scrutiny by the outside world than they currently receive: on one viewing, it's the biggest trove of tat conceived by mankind; on another, the birthplace of a New World Order of trade.

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