The islands in the East China Sea -- known as the Diaoyu in China and Senkaku in Japan -- are administered by Tokyo but claimed by Beijing and are a frequent hotspot in bilateral tensions.

China's foreign ministry said in a statement Sunday it had lodged "solemn representations" with the Japanese embassy's chief minister after "a civilian aircraft intruded into the airspace of the Diaoyu Islands", calling it an "illegal infringement activity".

A day earlier, the Japanese foreign ministry said in a statement that its vice minister lodged "a strong protest" with the Chinese ambassador to Japan "over the intrusion of four China Coast Guard vessels into Japan's territorial waters around the Senkaku Islands".

The vice minister also protested "the violation of Japan's territorial airspace by a helicopter launched from one of the China Coast Guard vessels, strongly urging (China) to ensure that similar acts do not recur".

Japan's defence ministry said the helicopter flew within Japanese airspace for about 15 minutes on Saturday near the Senkaku islands.

"The Self-Defence Forces responded by scrambling fighter jets," the ministry said.

Public broadcaster NHK and other local media reported that this is the first time a Chinese government helicopter violated the Japanese airspace off the disputed islands.

China's coast guard on Saturday announced it had used a helicopter to "expel" a Japanese aeroplane from airspace around the disputed islands.

Liu Dejun, a spokesperson for China's coast guard, said a Japanese civilian aircraft "illegally entered" the airspace of the islands at 11:19 am (0219 GMT) and left five minutes later.

Beijing frequently announces it has driven Japanese vessels and aircraft away from the islands, but Japanese officials have told AFP that Chinese authorities sometimes announce expulsions when none have occurred.

Unnamed Japanese officials told local media that Beijing was possibly reacting to a small Japanese civilian aircraft flying near the islands.

Chinese and Japanese patrol vessels in the East China Sea have routinely staged dangerous face-offs around disputed islands.

Tensions between China and other claimants to parts of the East and South China Seas have driven Japan to deepen ties with the Philippines and the United States.