Beijing said on Tuesday it had protested against Kuala Lumpur filing a submission with the United Nations last week seeking to establish the limits of Malaysia's continental shelf in the northern part of the disputed South China Sea.
Under the United Nations Convention on the Law of the Sea, any country can claim an exclusive economic zone up to 200 nautical miles from its shoreline. However, China claims most of the South China Sea, across which more than $3.4 trillion worth of goods are transported every year.
As a result, Malaysia, whose biggest trading partner is China, said in its submission, dated Dec. 12, that there were areas of potential overlapping claims beyond its own exclusive economic zone.
Beijing said Malaysia's submission "infringes on China's sovereignty, sovereign rights and jurisdiction, and also violates the basic principles of international law".
"China has lodged representations on the matter with Malaysia and also stated its position to relevant institutions of the U.N," the spokesperson's office of China's foreign ministry said in a faxed reply to a query from Reuters.
"China hopes to maintain communication with relevant sides and to handle this matter appropriately."
Malaysia's foreign ministry did not respond to a request for comment.
The South China Morning Post reported that Beijing has sent a diplomatic note to U.N. Secretary-General Antonio Guterres.
Malaysia and Vietnam in 2009 made a joint submission for a portion of the two countries' continental shelf in the southern part of the South China Sea.
A senior Vietnamese official said last month it could explore legal action, among various options, in its territorial dispute with China over the waters.
On Tuesday, Vietnam said it hoped China would show restraint in the South China Sea next year after a Chinese oil survey vessel and its escorts spent months within Vietnam's exclusive economic zone, in what Hanoi called a blatant violation of its sovereignty.
Vietnam, the region's most forceful challenger of China's extensive maritime claims to the busy waterway, will take on the rotating chairmanship of the Association of Southeast Asian Nations (ASEAN) in 2020.
The U.N. Commission on the Limits of the Continental Shelf said Malaysia's partial submission on the northern part would be included in the provisional agenda of its 53rd session, to be held in New York in 2021.
Malaysia had been critical of China's South China Sea position but has been less outspoken recently, especially after Beijing pumped billions of dollars into infrastructure projects under its Belt and Road Initiative.
But Malaysia's foreign minister said in October the country needed to boost its naval capabilities to prepare for possible conflict in the South China Sea.