China sends warplanes over disputed islands in East China Sea
A US Navy F/A-18 aircraft prepares to land on the runway of the US Navy aircraft carrier USS George Washington during a tour of the ship in the South China Sea - (Reuters)

China has sent several warplanes, including an early warning aircraft, into the newly declared air defence zone above disputed islands in the East China Sea after South Korea and Japan defied Beijing's order not to enter the airspace.

China had earlier declared a new air defence zone in the East China Sea comprising the disputed chain of islands, which Beijing calls Diaoyu and Japan Senkaku, adding a new dimension to the territorial row.

However, following the announcement, the US flew two B-52 bombers in support of its ally, Japan. Japan and South Korea soon followed suit by sending their military aircraft - directly defying Beijing's regulations which request prior permission from Chinese authorities before foreign planes can fly through..

The aircraft belonging to the US, Japan and South Korea flew without informing China in advance. But Beijing asserted it was aware of all the flights in the region as it continues to monitor them.

Shortly after the moves by South Korea and Japan, China swiftly sent its aircraft in what it claimed were routine exercises.

China's spokesperson Colonel Shen Jinke told the official news agency Xinhua that the latest deployment is "a defensive measure and in line with international common practices".

He added: "China's air force is on high alert and will take measures to deal with diverse air threats to firmly protect the security of the country's airspace."

It is still unclear whether the Chinese aircraft encountered any foreign jets that flew over the disputed zone. Japan has also not offered any confirmation about the Chinese aircraft but said its forces are on high alert.

The spokesperson for China's defence ministry Yang Yujun said it would be "incorrect" to suggest that China intends to shoot down any foreign aircraft entering the air defence zone without notice.

"We decline to comment on Chinese flights, but the United States will continue to partner with our allies and operate in the area as normal," a Pentagon spokesperson said, according to Reuters.