Chinese archaeologists discovered the cultural relics sites during a 400-km patrol, state-run Xinhua news agency reported.
The archaeologists examined 12 known cultural relic sites and found 12 new sites, collecting a large quantity of specimens, including ancient pottery and porcelain wares, copper coins and boat parts, said Li Jilong, an expert with the provincial cultural heritage bureau.
The Xisha Islands consist of a cluster of about 40 islets, sandbanks and reefs.
During ancient times, many Chinese merchant ships struck the reefs and sank while sailing to Southeast Asia, India and the Middle East, leaving abundant treasures and cultural relics in the sea, the report said.
The archaeologists also discovered that illegal salvaging of underwater cultural relics in the South China Sea has been rampant, and traces left by thieves in some relic sites show that large-scale thefts were conducted there early this year.
Today's report followed formation of a municipal council for a newly established city called Sansha in the Xisha, Zhongsha and Nansha as well as the formation of Sansha garrison command responsible for "national defense" and "military operations."
The Chinese government declared the establishment of Sansha last month, saying its role is to administer the island which Vietnam calls Paracel and Spratly archipelagos and surrounding South China Sea waters.
The islands are believed to hold oil and natural gas deposits and are also in whole or in part by Brunei, China, Malaysia, the Philippines, Taiwan and Vietnam.
Last week the Vietnamese government expressed its opposition to the establishment of Sansha. It called the move a "serious violation" of Hanoi's sovereignty over the Paracel and Spratly chains, which it claims as part of Danang city and Khanh Hoa province respectively.
China has also sent large ships to patrol the islands to prevent any fishing in the area by Vietnamese or other countries vessels.
