A towboat carrying a huge "steel box" left the port of Guangzhou in south China on Sunday morning to begin salvage work on an 800-year-old ship, the most precious ancient ship found so far in the world.

The towboat with the "steel box" will sail for two days before reaching the working waters, some 20 nautical miles west of Hailing Island of Yangjiang City in south China's Guangdong Province, according to the Guangzhou Daily.

The sunken ship, which dates back to the early Southern Song Dynasty (1127-1279), was the first ancient vessel discovered on the "Marine Silk Road" of the South China Sea and was named "Nanhai No.1", literally South China Sea No.1.

Nanhai No.1 was found by chance in 1987. The ship, more than 25 meters long, is the largest cargo ship from the Song Dynasty so far discovered. The total value of the shipwreck may be over US$100 billion.

Green glazed porcelain plates, tin pots, shadowy blue porcelains and other rare antiques have been found during the initial exploration of the ship. Archaeologists estimate that there are probably 50,000 to 70,000 relics on the ship, and that the archeological value of the Nanhai No.1 is no less than the terracotta warriors of Emperor Qinshihuang.

The "steel box" measures 35.7 meters in length, 14.4 meters in width and 12 meters in height, weighing 530 tons. It will be used to salvage the ship with two meters thick of silt that covers it together to better protect the precious relics.

After salvage, the ancient ship, with its silt, will be put in a huge glass pool, in which water temperature, pressure and other environmental conditions will be the same as on the sea bed where the ship has slept for 800 years.

Archaeologists will then conduct thorough excavations of the ship in the pool.

It is estimated that the ship will surface in mid-July, till then questions -- such as which port was the ancient ship's destination and how did it sink -- will be addressed by archaeologists.

(CRI May 6, 2007)