China expressed strong opposition on Friday to a decision by Japan and the Philippines to start maritime border negotiations, calling the talks "illegal" and claiming exclusive control over the waters concerned.

The two island nations announced on Thursday they would start formal talks "to delimit the maritime boundary" of an economic zone and continental shelf between them, as Philippine President Ferdinand Marcos met Japanese Prime Minister Sanae Takaichi on a visit to Tokyo.

But Beijing again asserted on Friday that it has an "exclusive economic zone and continental shelf" in the waters to the east of Taiwan.

"China is strongly dissatisfied with and firmly opposed to this," foreign ministry spokeswoman Mao Ning told a regular news conference when asked about the delimitation talks between Tokyo and Manila.

"China solemnly declares that the so-called delimitation negotiations between Japan and the Philippines are entirely illegal and invalid," Mao said.

Beijing has "lodged solemn representations" with both countries, she added.

Manila and Tokyo's shared grievances over Chinese maritime territorial claims have seen them draw increasingly close in recent years.

Japan and China are in territorial and economic disputes in the East China Sea, where coastguard ships from both sides routinely stage dangerous standoffs.

Beijing has meanwhile deployed navy and coast guard vessels in the South China Sea, in a bid to bar the Philippines from strategically important reefs and islands, leading to a string of confrontations.