China's top legislature strongly protested against Vietnam's "erroneous" new maritime law and urged its Vietnamese counterpart to make an "immediate correction".
Hanoi's disputes with Beijing in the South China Sea have given rise to frictions, and analysts said the passed law may internationalize the issue and bring a heavy blow to bilateral relations.
The Foreign Affairs Committee of The National People's Congress expressed its position concerning Vietnam's Thursday move in a letter to the Committee on Foreign Affairs of the Vietnamese National Assembly, Xinhua reported on Friday.
The Vietnamese Law of the Sea would include China's Xisha Islands and Nansha Islands in the South China Sea within Vietnam's so-called sovereignty and jurisdiction.
The NPC urged the Vietnamese lawmakers to pay substantial respect to China's territorial sovereignty, immediately correct its erroneous move and make due efforts to ensure the comprehensive strategic partnership between the two countries as well as the friendly relationship with its Chinese counterpart.
"It violates the consensus reached by leaders of both countries, as well as the principles of the Declaration on the Conduct of Parties in the South China Sea," the letter said.
China has indisputable sovereignty over the Xisha and Nansha islands and adjacent waters in the South China Sea, the NPC reiterated, asserting that Vietnam's move seriously infringed China's sovereignty and is illegal and invalid.
Chinese Vice-Foreign Minister Zhang Zhijun on Thursday summoned Vietnam's Ambassador to China Nguyen Van Tho to lodge a solemn representation.
Vietnamese Foreign Ministry spokesman Luong Thanh Nghi, however, said in a statement posted on the ministry's website late Thursday that Vietnam rejected China's protest.
The official Thanh Nien newspaper reported on Friday that the law will come into force in January 2013, AFP said.
Qi Jianguo, former Chinese ambassador to Vietnam, said Hanoi's Law of the Sea will not change the fact that China enjoys indisputable sovereignty and substantial control over the islands.
"Actually the Vietnamese National Assembly approved the Law on National Border in June 2003 to lay rival claim over China's Xisha Islands and Nansha Islands, yet the move made little difference," Qi said.
The South China Sea is believed to sit atop vast oil and gas deposits, and by passing the law, Vietnam is trying to involve more foreign countries and firms in resource exploration and development in the area, said Shu Zhenya, a researcher of China Institute for Marine Affairs under the State Oceanic Bureau.
"Hanoi wants to bundle up its interests with countries overseas, and the passed law provides a legal basis for internationalizing the South China Sea issue," Shu said in an online article.
Shu also urged a quickening of ocean-related legislation and administration to ensure China's maritime rights and interests.
As a move to improve administrative management on the islands, China has raised the administrative status of Xisha, Zhongsha and Nansha islands in the South China Sea from county level to prefectural level, according to an official statement from the Ministry of Civil Affairs on Thursday.