The pictures, taken by Planet Labs Inc., appear to show the Liaoning carrier at the centre of a formation of more than 40 other ships lined up in pairs south of China's Hainan province island on Monday.

China's defence ministry refused to confirm whether the Liaoning took part in drills this week but military experts say the aircraft carrier is identifiable.

Six submarines and two J-15 fighter jets appear to lead the "naval parade", James Char, a military expert at Singapore's Nanyang Technological University, told AFP.

"Such a formation serves more of as a visual spectacle with the Liaoning the status symbol of the PLA (People's Liberation Army)," Char said.

"This formation is unlikely to be used in actual combat situations," he said, adding that he would "not be surprised" if it was purposely aimed at being picked up by satellite images.

The show of force emerged days after Taiwan said that the Liaoning and other vessels had passed through the Taiwan Strait on March 20 -- the same day that Chinese President Xi Jinping warned against any attempts to divide China.

- Sea claims -

Beijing has also been asserting its vast claims to the South China Sea, transforming reefs into islands capable of hosting military equipment.

Brunei, Malaysia, the Philippines, Vietnam and Taiwan have their own claims to the sea, while US warships regularly conduct "freedom of navigation" operations near islands controlled by Beijing.

"We can expect the (Chinese naval) presence in the South China Sea becoming more regular, especially with the increase in freedom of navigation patrols by the United States as well as other countries," Char said.

Jeffrey Lewis, of the Middlebury Institute of International Studies, said that while it was a "large naval drill", past photos have shown the carrier "travelling in such a formation."

"It was probably transiting to a location," he said.

In another picture taken by Planet Labs on Tuesday, the Liaoning is seen south of Hainan island's Yulin Naval Base, but no longer in formation with other ships.

Defence ministry spokesman Ren Guoqiang confirmed on Thursday that the navy has conducted a "routine" drill in the South China Sea to improve the military's "capability to win wars".

"It is not targeted at any specific country or target," Ren told reporters, without saying how many and which ships were involved.

Separately, the air force had announced on Sunday that aircraft, including H-6K bombers and Su-35 fighter jets, had recently participated in a joint combat patrol mission in the South China Sea, according to the official Xinhua news agency, without giving more details.

China's government announced earlier this month an 8.1 percent increase in military spending to 1.11 trillion yuan ($175 billion).

The Liaoning is a Soviet-era vessel that was bought from Ukraine, refitted and commissioned in 2012.

Last year, China unveiled its first domestically-built aircraft carrier, which will carry J-15 fighters that will take off from a raised "ski jump" platform. It has yet to be put into operation.