China is to start removing treasures from its greatest ever marine archaeological discovery, six years after the wreck was raised from the seabed in a giant metal box, reports said Friday. The wooden Nanhai 1 sank near Yangjiang in the southern province of Guangdong during the Southern Song Dynasty of 1127-1279, with an estimated 60,000 to 80,000 items on board. For centuries it was preserved under the sea by a thick covering of silt, and it was discovered accidentally by a British-Chinese expedition looking for a completely different vessel, the Rhynsburg from the Dutch East India Company (VOC). The Nanhai 1 was salvaged in 2007, and its cargo of porcelain, lacquerware and gold objects is "more than enough to stuff a provincial-level museum", said the Southern Metropolis Daily. Since its recovery the merchant ship has been kept in the sealed-off steel container in a specially built glass-walled exhibition hall, the report said. The vessel's "full excavation" was officially launched Thursday and authorities expect to retrieve all its relics in the next three to four years, it said, citing Tong Mingkang, a deputy head of the State Administration of Cultural Heritage. Archaeologists plan to spend the first year clearing away the silt covering the ship and removing the most valuable items from the hold, the paper said. The excavation site will be open to the public one day every week, Tong was quoted as saying. More than 6,000 relics have previously been recovered, the report said. The vessel's exact route is not known, but it is believed to have been plying the so-called "Marine Silk Road" which linked China with India, the Middle East and even Africa in ancient times.