Now Chinese scientists want to awaken the ship from its slumber in the silt 20 nautical miles off the coast of Guangdong, which British sailors have long known as Canton. The treasure on board is truly amazing and impossible to value. Initial excavations have revealed beautiful green glazed porcelain plates, blue porcelain and tin pots, as well as chinaware specially designed for foreign markets. There could be anything up to 70,000 relics on the ship.

Some cultural relics experts in China say the value of the find could be equal to that of Emperor Qin Shi Huang’s terracotta warriors in Xian. Archaeologists believe the ship dates back to the second period of the Song Dynasty (1127-1279). At 25 metres (83ft) long and 10 metres (33ft) wide, it is the largest cargo ship from that golden period of Chinese merchant history discovered so far.

The overland Silk Road, which runs from western China to Europe, is probably a better known trading route. However, Chinese traders began selling silks, porcelain and tea along the Marine Silk Road about 2,000 years ago, from southern ports in Guangdong and Fujian to countries in South-East Asia, Arab countries and Europe.

The ship is well preserved, lying upright on the seabed with its hull hard and intact. In what promises to be a complex feat of engineering, the scientists want to use a huge steel basket to lift the vessel out in one piece, better to preserve its original looks. The ship is 20 metres below the waves.

They will then store it in a giant salt-water tank in a purpose-built museum. Discovered by accident in 1987, the merchant ship was named Nanhai No 1 (South China Sea No 1). Since then it has been pinpointed precisely using state-of-the-art global positioning system technology.

"It is unprecedented in the field of underwater archaeology, both at home and abroad," Zhang Wei, director of the Underwater Archaeology Centre at China’s National Museum, told the Xinhua news agency.

The usual procedure would be to dig up the relics and then salvage the vessel, but Mr Zhang said that the scientists wanted to move the ship still covered in silt to preserve the artefacts. Being buried in two metres of silt has done much to protect the Nanhai No 1, but it has also made excavation very difficult.

"We could see nothing in the water area, and could only work by touch in the silt," said Zhang Wanxing, an underwater archaeological expert.The silt made measuring, drawing and photographing the relics almost impossible, but draining the silt could damage the porcelain on board.

A salvage vessel to raise the Nanhai No 1 is being built and should be finished by May. The Guangdong provincial government has budgeted £11 million to build a museum and pride of place will be the "crystal palace" — a glass-walled exhibition hall, filled with sea water to house Nanhai No 1 in a similar undersea environment to the one in which it has lain for eight centuries.

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