China and Taiwan criticised Japan for giving Japanese names to disputed islands in the East China Sea claimed by all three parties in a long-running diplomatic row.
China and Japan have a lengthy dispute over an uninhabited but strategically coveted island chain known as Diaoyu in Chinese and Senkaku in Japanese.
Taiwan also claims the islands and local activists have tried to sail to the disputed area to press Taipei's claim.
China's foreign ministry on Saturday said moves by Japan to rename scores of islands in the chain was "illegal and invalid", according to a statement posted on the ministry's website.
"No matter what names Japan has given to the islands affiliated to Diaoyu island, it will not change the fact that these islands belong to China," Chinese foreign ministry spokesman Hong Lei said in the statement.
China's State Oceanic Administration has released names in Chinese for the islands in the chain, which it put at 70, the official Xinhua news agency said Saturday.
Separately, Taiwan protested to Japan for renaming four islets in the contested chain and unveiling the names on Friday.
"We have lodged a stern protest and reaffirmed our stance that the Diaoyu islands are part of our territory," Taiwan's foreign ministry said.
Japan has said it plans to finish naming 39 uninhabited islands by the end of March.
The islands, which are believed to be surrounded by oil and gas reserves, have long been a source of friction between China, Japan and Taiwan.
China considers Taiwan to be part of its territory and has long sought political reunification with the island. Japan officially recognises China rather than Taiwan but maintains close trade ties with the island.