Shanghai plans to build a vast underground network of malls, restaurants and parking lots to make up for a lack of space above ground according to a recent government report. The development will cover 600,000 square meters, the equivalent of 120 soccer fields spread across four underground floors, the city government reported on its website. The city is accepting bids from builders. Shanghai has about 20 million people plus factories, office towers and high-rise apartments crowded into a small triangular territory near the mouth of the Yangtze River. The plans call for the project due to be finished by 2006 to expand existing facilities scattered along Shanghai's subway system. The project will need advanced technology to supply fresh air and ensure safety. But the biggest concern is the stability of the soil under the city. Shanghai is sinking by 1.5 centimeters a year. Land subsidence has been aggravated by over-pumping of underground water and the construction of thousands of high-rise buildings. "Shanghai's foundations are built on soft soil, so building multistoried spaces underground would be like digging holes in a piece of bean curd," the government reports said,"the difficulties are easy to see".