BEIJING (REUTERS) - China's first aircraft carrier has successfully finished a series of tests during a training mission in the disputed South China Sea and has returned to port, state media reported.

Last month's drills off the coast of Hainan Island marked not only the first time China has sent a carrier into the South China Sea but the first time it has manoeuvred with the kind of strike group of escort ships US. carriers deploy, according to regional military officers and analysts.

After two decades of double-digit increases in the military budget, China's admirals plan to develop a full blue-water navy capable of defending growing economic interests as well as disputed territory in the South and East China Seas.

The aircraft carrier Liaoning carried out more than 100 tests, including of its combat systems, and has now docked at port in the northern city of Qingdao, the official Xinhua news agency said late on Wednesday.

"The aircraft carrier underwent a comprehensive test of its combat system and conducted a formation practice during its 37-day voyage," Xinhua said, citing an unnamed naval source as saying.

The tests "attained the anticipated objectives", the report added. "All tests and training programmes went well as scheduled." The carrier was escorted by two destroyers and two frigates, and aircraft and submarines also participated in the drills.

The Liaoning - a Soviet-era ship bought from Ukraine in 1998 and re-fitted in a Chinese shipyard - has long been a symbol of China's naval build-up.

Carrier strike groups sit at the core of China's naval ambitions and successfully operating the 60,000-tonne Liaoning is the first step in what state media and some military experts believe will be the deployment of locally built carriers by 2020.

Friction over the South China Sea has surged as China uses its growing naval might to assert a vast claim over the oil-and-gas-rich area, raising fears of a clash between it and other countries in the region, including the Philippines and Vietnam.

The USS Cowpens narrowly avoided colliding with a Chinese warship escorting the Liaoning while operating in international waters on Dec 5, the U.S. Navy has said.

Xinhua said the Cowpens was "warned" by the carrier task force, adding the U.S. vessel was "intentionally" putting the Liaoning under surveillance.

BEIJING (CHINA DAILY/ASIA NEWS NETWORK) - The Chinese navy released on Wednesday the first photographs of what many military observers believe is the Liaoning aircraft carrier battle group as the nation's first aircraft carrier returned to its homeport of Qingdao, Shandong province.

The photos show the Liaoning sailing with several battleships, submarines and military aircraftperforming a series of drills. The navy did not disclose when and where they were taken.

The carrier had successfully carried out 37 days of tests and training exercises in the South China Sea and returned to a People's Liberation Army's naval base in Qingdao, the navy said ina statement released on Wednesday.

"During the mission, the Liaoning conducted more than 100 drills and training exercises. Thedrills tested the structure's stress resistance, sailing speeds in deep water, navigationalcapabilities and weapons and equipment reliability," the statement said.

The Liaoning left Qingdao on Nov 26 and was anchored at a naval base in Sanya, Hainan province, three days later. On Dec 5, it set out on the training mission.

This is the carrier's first long-distance training voyage since it was commissioned in the PLA navy last year.

The carrier completed its first comprehensive combat training during the mission and performeda formation drill with other Chinese ships and submarines in the battle group, another first for the Chinese navy, the statement said.

Two missile destroyers, the Shenyang and Shijiazhuang, and two missile frigates, the Yantai and Weifang, participated in the mission. They escorted the carrier from Qingdao to Sanya.

The use of four ships led military observers to speculate that the navy's carrier battle group has taken shape with the Liaoning as its core.

But experts from the PLA said the four ships are not enough to protect the carrier.

Li Li, a professor with PLA National Defense University, said that Chinese destroyers are smaller in size and tonnage than their foreign counterparts and are thus incapable of carrying a large arsenal of weapons.

She said the Chinese navy will procure and deploy bigger destroyers of around 10,000 metric tons.

In addition to formation training, the military is training its pilots for the carrier-based J-15 fighter aircraft, said Wang Ya'nan, deputy editor-in-chief at Aerospace Knowledge magazine.

"Pilots must pass a set of sophisticated training drills before becoming qualified to take off and land on a carrier. The course usually takes at least two years," said Wang, who added that a lack of experience and J-15s could prolong the training needed for China's pilots to be capable of serving on carriers.