CHINA will soon build the world's first so-called Archimedes bridge across Qiandao Lake in Zhejiang Province, Xinhua news agency reported today.

When completed, the 100-meter-long bridge will be submerged in the water. It will look like an oval tube from outside. Inside it, two layers of one-way motorways will run though in the middle, with two railway tracks flanking them, the report said.

The site of the prospective bridge was unveiled yesterday at an exhibition held at the Chinese Embassy in Rome, the report said.

The bridge itself can produce enough buoyancy to stay afloat. Therefore anchors and steel cables will be used to attach it to the lake bottom, the report said.

This project is based on the Archimedes law, from which the bridge derives its name. It can also be called a suspended tunnel or submerged floating tunnel, the report said. The law, or Archimedes' principle as it is sometimes referred, states that an object immersed in fluid loses weight equal to the weight of the amount of fluid it displaces.

The Archimedes bridge is expected to have a bright future as a state-of-the-art architectural technique. Compared with other traditional techniques like suspension bridges and sunken tunnels, it is cheaper to build and produces less pollution, the report said.

Though the technique can be widely used in places like straits and inland seas, it still has to overcome some technical problems, the report said.

The Sino-Italian cooperation culminated in a treaty signed in 2004 between the Institute of Mechanics of Chinese Academy of Sciences and the Italian Archimedes Bridge Company, which paved the way for future construction of the bridge.