An activist holds the Japanese flag before a group placed the country's flag on a disputed island, part of a group known as Senkaku in Japanese and Diaoyu in Chinese.
Credit: Antoine Bouthier

China announced Saturday that it was creating an air defense zone that encompasses a disputed chain of islands owned by Japan.

The Chinese defense ministry said that an aircraft entering the zone must notify the Chinese authorities before doing so.

Those non-commercial aircraft that don't follow the rule over the East China Sea will be subject to "emergency military measures."

China said it would "identify, monitor, control and react" to any threats coming into the zone unidentified, marked on this map.

The rules go into effect on Saturday.

The declaration caused an uproar in Japan

Japan called China's ambassador in the country to tell them that the creation of the area was "totally unacceptable."

"By establishing the air-defense zone Beijing has ... potentially escalated the danger of accidental collisions between the Chinese military and the US and Japanese counterparts," said an advisor to Japanese Prime Minister Shinzo Abe.

"It poses a serious challenge against freedom of movement in the sky and in the seas."

Taiwan, which also claims the islands, expressed its unhappiness about the situation.

South Korea also claims the islands, off the coast of which there is believed to be oil and gas deposits.

China's increasing military clout has increased tensions with neighboring countries like Japan and the Philippines over its martime claims.

Both China and Japan lay claim to the islets known as Diaoyu in Chinese and Senkaku in Japanese.

Tensions over the islands have increased over the last year after the Japanese bought some of the rocks from private Japanese owners.

China refused to accept the deal and the two sides have traded barbs and threats since then.

"This is a necessary measure taken by China in exercising its self-defense right," Chinese Defense Ministry spokesman Yang Yujun said about the creation of the air defence zone. "It is not directed against any specific country or target. It does not affect the freedom of over-flight in the related airspace."

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