China says it reserves the right to respond to a decision by a Japanese city to rename the administrative area that includes remote islands claimed by both China and Japan and have long been a source of friction between the neighbors.
The row over the uninhabited East China Sea islets may add to recent tension caused by Japan's criticisms of Beijing's plan to impose a new national security law in Hong Kong. China has said Japan should not interfere in Beijing's internal affairs.
The disputed islands are known as the Senkaku in Japan and the Diaoyu in China and Taiwan.
Japanese broadcaster NHK reported earlier that the Ishigaki City assembly in Okinawa, in southern Japan, had passed a bill to change the name of the administrative area covering the islands to Tonoshiro Senkaku from Tonoshiro, from October 1.
NHK said the name had been changed to avoid administrative mistakes as another location in Ishigaki City was also called Tonoshiro.
The uninhabited islands are at the center of a festering row between Tokyo and Beijing and the move by the small local council -- which does not carry national governmental weight -- sparked anger in both Taiwan and mainland China.
"The passing of the so-called administration designation bill by Japan is a serious provocation to China's territorial sovereignty," Chinese Foreign Ministry spokesman Zhao Lijian said in response to a question on the issue.
"It is illegal and invalid, and cannot change the fact that the Diaoyu islands belong to China," Zhao added, saying Beijing had lodged "solemn representations to Japan through diplomatic channels and reserves the right to make further responses."
Taiwan's government, which also claims the islets, also said its foreign ministry had "strongly protested" to Japan about the name change.
"The sovereignty of Diaoyu islands belongs to our country and any move attempting to alter this fact is invalid," the foreign ministry said in a statement.
It said it had expressed "regret and stern protest" to Tokyo.
Japan's chief government spokesman declined to comment on the Ishigaki council move, but Tokyo has long complained about China's routine dispatch of its coast guard ships to waters surrounding the islands.
Relations between Japan and China deteriorated in 2012 when Tokyo "nationalized" some of the disputed islets and tensions have flared up periodically over the region.
(Source: Agencies)