Commissioned in 2019, the more than 300-metre (1,000-foot) Shandong is China's second carrier and key to the country's regional ambitions under President Xi Jinping, who oversaw a massive naval buildup that has rattled Asian neighbours.

Beijing earlier announced the Shandong and its escort vessels -- which include the destroyer Zhanjiang and frigate Yuncheng -- will visit the Chinese finance hub for five days and host "tours and cultural exchange activities".

The flotilla was spotted early on Thursday morning sailing off the southern coast of Hong Kong island.

The Shandong's visit came days after it concluded combat drills in the western Pacific, alongside China's first aircraft carrier the Liaoning.

Both ships are of a modified Soviet design with a distinctive "ski jump" deck for aircraft takeoff.

China's third and more advanced carrier, the Fujian, is undergoing sea trials.

Tickets to visit the vessels in Hong Kong were snapped up within minutes on social media app WeChat.

"The idea appears to impress upon the Hong Kong public... the ruling (Chinese Communist Party's) quest for building what's termed as the status of a maritime great power," said Collin Koh, a naval affairs specialist at the S. Rajaratnam School of International Studies in Singapore.

The Shandong is the second Chinese aircraft carrier to visit Hong Kong, following a 2017 visit by the Liaoning.

China has rapidly upgraded its naval forces as it seeks to expand its reach in the Pacific and challenge a US-led alliance.

The US Department of Defense said in a December report that numerically China has the largest navy in the world, with a battle force of more than 370 ships and submarines.

Japan authorities said China's dual-carrier exercise in the Pacific last month was the first of its kind and reflected intentions to improve operational capabilities in distant areas.

Chong Ja Ian of the National University of Singapore said China's latest exercises suggest "both aircraft carriers are ready to engage in more sophisticated operations" but some unknowns remain, including the operational tempo they can bear.

In April, the Shandong took part in drills testing the Chinese navy's ability to "blockade" Taiwan, according to the Eastern Theater Command.

China insists that the self-ruled democracy is part of its territory and has refused to rule out seizing it by force.

The Shandong was also reportedly present in Philippine waters in April during a joint US-Philippines military exercise, deepening tensions between Manila and Beijing.