Shanghai announced the kickoff of an archaeological excavation of a shipwreck site at the mouth of the Yangtze River on Wednesday.

The shipwreck, known as Boat No 2 on the Yangtze River Mouth, is "the largest and best-kept, with the largest number of cultural relics on board in China's underwater archaeological findings", said Fang Shizhong, director of Shanghai Municipal Administration for Culture and Tourism.

The merchant ship, dating to the reign of Emperor Tongzhi (1862-1875) in the Qing Dynasty (1644-1911), sits 5.5 meters below the ocean bed at a shoal on the northeast tip of Hengsha Island in Chongming district.

Archaeologists found that the boat is about 38.5 meters long and 7.8 meters wide at its broadest. A total of 31 cargo chambers were detected, with "piles of ceramic objects made in Jingdezhen, Jiangxi province, and purple-clay wares from Yixing, Jiangsu province," said Zhai Yang, deputy director of Shanghai Center for the Protection and Research of Cultural Relics.

The Shanghai Municipal Cultural Heritage Administration began conducting a survey of the city's underwater cultural heritage in 2011, and the shipwreck was found in 2015.

The muddy water, complicated seabed conditions, as well as busy traffic on the sea brought challenges to the investigation and excavation of the boat, said Zhou Dongrong, deputy director of the Ministry of Transport's Shanghai salvage bureau. The bureau adopted the technologies of shield-driven tunnel digging, which was widely used in Shanghai's construction of subway routes, and combined it with a new system consisting of 22 giant arch-shaped beams that will reach under the shipwreck and scoop it out of the water, along with the mud and attached objects, without contacting the ship's body.

Such an innovative project "shows the collaborative development in China's protection for its cultural relics and technological improvement", said Wang Wei, president of the Chinese Archaeological Society.

The excavation is expected to be completed later this year, when the whole shipwreck will be placed on a salvage ship and transported to the Huangpu River bank in Yangpu district. A maritime museum will be built there for the shipwreck, where the cargo, boat structure and even the mud attached to it will be subjects of archaeological research, Zhai told media on Tuesday.

Fang said it is the first case in China in which excavation, research and museum construction is being carried out simultaneously for a shipwreck.

"The shipwreck is tangible evidence illustrating Shanghai's historical role as a shipping and trade center for East Asia, and even the whole world," he said. "The important archaeological finding of it expanded our understanding of history, and brought to life historical scenes."