The Chinese Foreign Ministry strongly objected to what it called the Japanese F-15 fighters' attempt to intercept the Chinese patrol plane Thursday. Japan charged China entered its airspace with its plane over one of the Senkaku Islands in the East China Sea, which China also claims, referring to them as Diaoyu Islands.
There have been a number of instances in the past when China has sent patrol boats to the islands to assert its claims but Thursday's incident was the first time for what Japan called an airspace intrusion.
"Flying a marine surveillance airplane in airspace above the Diaoyu Islands is completely normal. China urges Japan to stop illegal actions in the waters and airspace of the Diaoyu Islands," Foreign Ministry spokesman Hong Lei said.
China Daily, quoting observers, reported Friday the situation remained under control, "but Tokyo seems intent on upping the ante."
The Japanese government said the Chinese government airplane entered Japanese airspace over the islands, following which Japan's Air Self-Defense Force sent the F-15 fighter jets to the area.
Japan also lodged a protest with China over the incident, Kyodo News reported.
The uninhabited Senkaku Islands are currently under Japanese control. Tensions between China and Japan over their respective territorial claims to the islands have escalated sharply since Japan nationalized the islands in September, leading to widespread and violent protests in Chinese cities to assert Beijing's claims with calls to boycott Japanese goods.
The official Xinhua News Agency, quoting Chinese maritime authorities, said a B-3837 marine surveillance plane was sent to "join vessels patrolling the territorial waters around the Diaoyu Islands on Thursday morning."
The report said the plane arrived in the area at about 10 a.m. and conducted joint patrols with a fleet of four surveillance ships, and that the fleet declared "the Chinese government's stance and ordered the Japanese ships that had entered China's territorial waters to leave the area immediately."
Japan's Chief Cabinet Secretary Osamu Fujimura called the six-hour-long incident Thursday "extremely deplorable" the airspace intrusion came on top of similar acts by Chinese ships.
"We are determined to deal firmly with action that violates our country's sovereignty in accordance with domestic laws and regulations," he said.
Separately, Japanese Prime Minister Yoshihiko Noda pledged to protect the nation and its people "by practicing a thorough crisis management to protect our territorial land, sea, sovereignty and national interests."
Kyodo reported six F-15s from a base on the main Okinawa Island were scrambled and routed two more already been airborne, but that the Chinese plane had already left the airspace when the fighter jets went there.
Japanese studies Professor Wang Xinsheng at Peking University told China Daily that Japan has been trying to play up its so-called "actual control" over the islands airspace to fool the international community.
The incident comes ahead of Japan's Sunday elections to the lower house of Parliament. Latest polls indicate the Liberal Democratic Party, currently the main opposition to Prime Minister Noda's ruling Democratic Party of Japan, would win handily. Former Prime Minister Shinzo Abe, who will return to his post if LDP winds, takes a tough stand on the island issue.
The United States, a close ally of Japan, has said it does not take a position on the island dispute but wants the issue resolved peacefully. However, the Senkaku Islands come under the scope of a 1960 US-Japan security treaty that calls for U.S. military support to Japan.
The East China Sea Senkaku Islands dispute is getting tenser even as China, with its growing military, continues to make aggressive claims to much of the South China Sea, a vital sea lane for international commerce. The South China Sea claims have raised deep concerns among smaller nations in the region, some of whom also have overlapping claims.
China refuses a multilateral approach, preferred by the United States, to resolve the South China Sea disputes and insists on a bilateral solution. But critics say a bilateral approach would allow China to bring pressure on countries dependent on it economically.