China sent its sole aircraft carrier on a training mission into the South China Sea on Tuesday amid maritime disputes with the Philippines and other neighbours and tension over its plan to set up an airspace defence zone in waters disputed with Japan.

A day earlier, the U.S. flew two B-52 bombers over disputed territory in the East China Sea without alerting China, the Wall Street Journal reported. The move was seen as a challenge to China's recent expansion of its Air Defence Identification Zone in those waters. China announced on the weekend that it was expanding the zone to include a chain of islands claimed by both China, which calls them Diaoyu, and Japan, which calls them Senkaku.

It issued a map of the expanded zone and new rules specifying that all aircraft entering the region must notify Chinese authorities and are subject to emergency military measures if they do not identify themselves or obey Beijing's orders.

South China Sea a key flashpoint

China also claims almost the entire oil- and gas-rich South China Sea, conflicting with claims from Taiwan, Malaysia, Brunei, the Philippines and Vietnam.

That dispute is one of the region's biggest flashpoints amid China's military build-up and the U.S. strategic "pivot" back to Asia, and Tuesday's deployment of the Liaoning aircraft carrier to the region is likely to exacerbate those tensions.

The Liaoning, bought used from Ukraine and refurbished in China, has conducted more than 100 exercises and experiments since it was commissioned last year, but this is the first time it has been sent to the South China Sea.

The Liaoning left port from the northern city of Qingdao accompanied by two destroyers and two frigates, the Chinese navy said on an official news website.

While there, it will carry out "scientific research, tests and military drills," the report said.

"This is the first time since the Liaoning entered service that it has carried out long-term drills on the high seas," it added.

Australia also concerned over expansion

The timing of the drills is bound to raise eyebrows with China's neighbours, given the overlapping maritime disputes. China has lodged formal protests with the United States and Japan after both criticized its plan to impose new rules on airspace over disputed waters in the East China Sea.

On Tuesday, Australia said it had summoned China's ambassador to express concern over its imposition of the Air Defence Identification Zone.

Analysts say Beijing might have miscalculated the forcefulness and speed with which its neighbours rejected its demands.

Washington, which has hundreds of military aircraft based in the region, says it has zero intention of complying. Japan likewise has called the zone invalid, unenforceable and dangerous, while Taiwan and South Korea, both close to the U.S., also rejected it.

'Not overly concerned'

Though considered decades behind U.S. technology, the Liaoning represents the Chinese navy's blue-water ambitions and has been the focus of a campaign to stir patriotism.

Rommel Banlaoi, executive director of the Philippine Institute for Peace, Violence and Terrorism Research, said he thought the Liaoning was still years away from representing a real threat.

Japan China East China Sea

A chain of disputed islands in the East China Sea, called Senkaku by Japan and Diaoyu by China. The Chinese Defence Ministry on Saturday issued a new map of the East China Sea Air Defense Identification Zone that includes the islands, triggering a protest from Tokyo, the U.S. and other countries with interests in the region. (Kyodo News/Associated Press)

"China is still developing its own model of carrier operations and its technology is (far) behind the United States," he said. "Personally, I would not be overly concerned with an old diesel-powered aircraft carrier on a training mission."

The navy did not specify exactly what training would be done, only noting that previous exercises involving aircraft landing and taking off had gone well.

Previously reported training exercises have mostly been in the Yellow Sea, between China and the Korean peninsula.

"Obviously, the Chinese authorities have been adopting a series of measures to strengthen their claim on the sovereignty of the disputed territories," said Joseph Cheng, a political science professor at City University of Hong Kong.

"You see Japan and Southeast Asian countries have also been making gestures and taking steps to strengthen sovereignty, so China has to respond."

China's navy said the mission was routine, adding that the Liaoning was still in a testing phase.

"This test visit to the South China Sea is part of normal arrangements for testing and training for the Liaoning," it said.

"Long cross-sea voyages are a necessary stage of experimentation and training to test equipment and troops under continuous work and different hydrological and meteorological conditions." 

With files from The Associated Press, CBC News