State-run Xinhua News Agency reported an unknown number of crewman were pulled safely from the waters of the South China Sea after their fishing boat capsized near the Xisha Islands.
Vietnam, the report said, has sent several ships to the area to interfere with operations undertaken by the China National Offshore Oil Corp. The Chinese government has formally asked the Vietnamese to refrain from such destructive activity, Xinhua added.
Vietnam contests the activity, saying CNOOC is operating in its territorial waters.
Last week, the Vietnamese National Assembly said the CNOOC decision to deploy rig HD-981 about 120 miles off the coast of Vietnam is a serious violation of its sovereignty and international laws.
China is at odds with most of its neighbors in the Asia-Pacific over claims to the maritime territory. More than 140 people were injured during mid-May demonstrations against China in Vietnam.