State media did not specify when the exercises with the Liaoning and Shandong vessels took place, though it said the broader naval mission had overlapped with public holidays that spanned late September to October.

The drills "in an area of the South China Sea" intended to "hone and enhance the combat capability of the aircraft carrier formation system," state broadcaster CCTV said.

In a post accompanied by a video of jets taking off from and landing on the two carriers, CCTV said the exercises also took place in the Yellow Sea and the East China Sea.

The Soviet-built Liaoning is China's oldest aircraft carrier, having been commissioned in 2012.

The Shandong entered service in 2019, while a third carrier, the Fujian, is undergoing sea trials.

The Liaoning this month took part in large-scale military exercises held around Taiwan, in what Beijing framed as a practice run for a blockade of the self-ruled island.

One expert told AFP the dual carrier exercise may have taken place following those drills -- and that they "represent a significant step forward in its carrier programme and power projection capabilities".

"We will certainly see more such exercises in the future, and China may incorporate both carriers into larger-scale Taiwan blockade exercises," said Duan Dang, a Vietnam-based maritime security analyst.

China has stepped up a massive expansion of its naval forces in recent years as it seeks to expand its reach in the Pacific and challenge a US-led alliance.

A January report by the US Congressional Research Service, citing the Pentagon, described it as the largest navy in the world and said it projected it to grow to 435 ships by 2030.

Analysts at Washington-based think tank CSIS have said the Fujian is expected to feature more advanced take-off systems, allowing the Chinese air force to deploy jets carrying larger payloads and more fuel.