The Chinese air force scrambled jets to follow US and Japanese planes as they flew through their new "air defense zone" over some disputed islands in the East China Sea.

Meanwhile, the US government is urging airlines who will be approaching the zone to file flight plans with the Japanese government.

Guardian:

China scrambled fighter jets to investigate US and Japanese aircraft flying through its new air defence zone over the East China Sea on Friday as the regional clamour over the disputed airspace escalated.

The ministry of defence announced the move, which is the first time China is known to have sent military aircraft into the zone alongside foreign flights, stepping up its response to the challenge after its unilateral establishment of the zone. It previously said it had monitored US, Japanese and South Korean aircraft and had flown routine patrols in the area on Thursday.

The ministry's statement said two US reconnaissance aircraft and 10 Japanese early warning, reconnaissance and fighter planes had entered the zone.

The airforce "monitored throughout the entire flights, made timely identification and ascertained the types", defence ministry spokesman Shen Jinke told the official China News Service.

The Pentagon has yet to respond to the statement. Japanese officials declined to confirm details of any flights, saying that routine missions were continuing.

Late on Friday the US state department advised American commercial airlines to notify Chinese authorities of flight plans over the East China Sea. But a US administration official said that did not mean Washington accepted Beijing's jurisdiction, the Reuters news agency reported.

"The US government generally expects that US carriers operating internationally will operate consistent with Notams [Notices to Airmen] issued by foreign countries," the state department said in a statement.

"Our expectation of operations by US carriers consistent with Notams does not indicate US government acceptance of China's requirements."

The developments came as South Korea's Yonhap news agency said officials were discussing how to expand its own air zone.

In Taiwan, legislators issued an unusual joint statement chiding Ma Ying-jeou's government for its tempered response to China's announcement of the zone and urging it to lodge a tough protest with Beijing. The government later said it would convey its "stern position".

Earlier the European Union's foreign affairs chief Catherine Ashton expressed its concern that the zone had contributed to tensions in the region, saying that the EU called on all sides to exercise caution and restraint.

Foreign ministry spokesman Qin Gang urged the EU to handle the situation "objectively and rationally", adding: "European countries can have air defence identification zones. Why can't China?"

The potential for miscalculation is growing. Plus, it's never good when warplanes from two potentially hostile countries occupy the same air space.

That said, China has no intention of going to war and neither do the other parties to the disputed area. China, which has spent a lot of cash on its navy and naval air power in the last decade, appears to be flexing its muscles a bit. In effect, they are announcing to the US, Japan, and other regional powers - "we're here and we're not going to go away."

Note how touchy Taiwan is about this. China is building up its navy to give it the option of invading Taiwan and forcibly taking it back. The Taiwanese are under no illusions about China's ultimate goal - and neither should we be.