The two ports handle most container traffic and represent key transit and storage hubs. Since September the volume of goods has dropped, reflecting the decline in exports and the fall in industrial output in the Yangtze River and Pearl River deltas.

Currently, China is experiencing its worst slump in exports in the past ten years. But for the government only 30 of economic activity is dependent on exports, so it is trying to stimulate internal demand to pick up the slack. Imports in December were also down by 21.3 per cent over last year.

According to experts the exports and imports are interdependent. In fact more than half of China's exports are made up of goods which are simply assembled in the country with components brought in from overseas, so as exports drop, the need for those components falls.

Still China’s trade balance remains positive. Last month exports were worth US$ 111.2 billion, and imports worth US$ 72.2 billion. Moreover, steep falls in world commodity and energy prices made imports cheaper for China.

But taken together these figures are worrying the authorities because they are further sign that economic activity is slowing down, which could spell bad news for employment levels and lead to social unrest.

Indeed expectations are not very rosy. In December Shenzhen outward-bound throughput of laden containers dropped 23 per cent year on year; a sign that exports will decline further. The 14.2 per cent growth of 2007 and 16.2 per cent expansion of 2006 are already distant memories.

But Shanghai's container throughput grew 6.8 per cent, making it the world's second-busiest container port behind Singapore.

Also the container throughput of the country's seven major international trading ports—Shanghai, Shenzhen, Qingdao, Tianjin, Ningbo, Xiamen and Dalian—grew 8.5 per cent last year (but down compared to 19.8 per cent in 2007 and 21.5 per cent in 2006).