Dozens of naval vessels and an aircraft carrier entered the vital trade waterway off Hainan island as part of what the Chinese navy had described as combat drills which were part of routine annual exercises.
The images, provided to the Reuters press agency by Earth imaging company Planet Labs Inc, show what appear to be at least 40 ships and submarines flanking the carrier, Liaoning.
It was described by some analysts as an unusually large display of the Chinese military’s increasing naval might.
The flotilla sailed in a line formation more suited to visual propaganda than hard military manoeuvres.
It was headed by what appeared to be submarines and supported by aircraft above.
The carrier group traversed the Taiwan Strait last week, according to Taiwan's defence ministry.
The flotilla's destination was unclear and the length of its operation unknown.
While the Liaoning has previously entered the South China Sea as part of drills in uncontested training grounds south of Hainan, its annual exercises are closely watched by regional and international powers analysing Beijing’s growing military might.
Jeffrey Lewis, a security expert at the California-based based Middlebury Institute of Strategic Studies, told Reuters that the images showed the first confirmation that the carrier was joining the drills.
“It’s an incredible picture,” he said. “That’s the big news to me. Confirmation that, yes, the carrier participated in the exercise.”
Collin Koh, a security expert at Singapore’s S Rajaratnam School of International Studies, described the deployment as unusual for its size and scope.
“Judging by the images, it does seem they are keen to show that elements of the South Sea Fleet are able to routinely join up with the carrier strike group from Dalian in the north,” he said.
“It does seem they want to show inter-fleet interoperability – something the [Chinese] navy has been quietly working on for some time.”
China’s air force said drills in the disputed sea and the Western Pacific were the best preparation for war.
The air force said H-6K bombers and Su-30 and Su-35 fighters, among other aircraft, carried out combat patrols over the South China Sea and exercises in the Western Pacific after passing over the Miyako Strait, which lies between two southern Japanese islands.
In recent years, China’s navy and coast guard forces have expanded rapidly and now patrol vast swathes of the South China Sea.
However, little is known about their combat readiness and coordination.
China’s claims in the South China Sea are disputed by Vietnam, the Philippines, Malaysia and Brunai. Taiwan also has claims.
The exercises come amid fresh signs of tension in the resource-rich waterway, with Vietnam recently halting oil exploration off its coast by Spanish firm Repsol following pressure from Beijing.
China also objected to a so-called freedom of navigation patrol by a US Navy destroyer last week close to one of its artificial islands in the Spratlys archipelago further south.
Beijing condemned America for what it called a "serious political and military provocation" after the USS Mustin sailed within 12 nautical miles of the Mischief Reef.
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