The 36,000-tonne Hainan is a helicopter-carrying amphibious assault ship that was hailed as a breakthrough for China's navy when it came into service in 2021.

It is part of the fleet that operates in the South China Sea, the site of multiple simmering territorial disputes between Beijing and its neighbours.

The hulking vessel was docked at a Hong Kong Island pier on Thursday, with multiple helicopters parked on its large, flat deck.

China's defence ministry this week said it was there to showcase the country's "military development" and the People's Liberation Army's (PLA) "firm determination and strong capabilities in safeguarding national sovereignty and security".

One expert told AFP its presence in Hong Kong was a deliberate reminder of China's authority there, after the quashing of the city's pro-democracy movement with a sweeping national security law in 2020.

"Sending some of the most powerful Chinese warships for public view in Hong Kong, in a way, symbolises and signals the very fact that (China's) government is behind the Hong Kong SAR government," Collin Koh, senior fellow at the S Rajaratnam School of International Studies, told AFP.

Along with the guided-missile destroyer Changsha, the Hainan will stay in the city for five days.

More than 10,000 people are expected to visit through invitation-only events, local media said.

The Hainan is one of three active warships of its type, and was spotted in the western Pacific near Japanese waters in August.

Over 200 metres long, the vessel can reportedly carry 30 helicopters, with the flight deck able to operate six at a time.

It represents "a milestone for the growing PLA amphibious assault capabilities", said Koh, increasingly important as tensions in both the South China Sea and the Taiwan Strait ramp up.

"Many will speculate that this ship (would) come in as a very important piece of capability when it comes to, say, a full-scale invasion of Taiwan itself," he said.