Vietnam on Thursday accused a Chinese survey vessel and its escorts of violating its sovereignty, and demanded that Beijing remove the ships from its waters.
Vietnam and China have long been embroiled in a territorial dispute over a potentially energy-rich stretch in the South China Sea, a strategic waterway through which more than US$3 trillion (about RM14 trillion) of commerce passes annually.
"Vietnam demands that China immediately remove the survey ship Xiang Yang Hong 10, Chinese coast guard ships and fishing vessels out of Vietnam's waters," foreign ministry spokesperson Pham Thu Hang said in a government statement.
"Vietnam has made contact with China several times and implemented measures in accordance with international law and Vietnamese law to ensure lawful and legitimate rights and interests of Vietnam," the statement added.
The Chinese embassy in Hanoi did not immediately respond to a request for a comment.
Last week Vietnam criticised recent conduct by a Chinese research ship in the same area of the Southeast Asian country's Exclusive Economic Zone (EEZ).
China has said that scientific research is a normal activity in areas under Chinese jurisdiction.
China claims almost the entire South China Sea as its territory, based on what it says are old maps, including waters that lie within Vietnam's EEZ and four other Southeast Asian countries.
Hang also said Vietnam called on the international community to join its efforts in maintaining order, peace and security in the South China Sea and contributing to the development of the two countries' mutual interests.