BEIJING (AFP) - A Chinese aircraft carrier is steaming towards Hong Kong for celebrations marking 20 years since Britain gave back the former colony, in a clear display of China's military might.

China's national defence ministry said Thursday (June 29) that the Liaoning was part of a flotilla on a "routine training mission" and would make a port of call in Hong Kong.

The Liaoning, a second-hand Soviet ship built nearly 30 years ago and commissioned in 2012, will arrive at a time when fears are growing that Beijing is tightening its grip over the semi-autonomous city.

President Xi Jinping arrived on Thursday amid tight security in the normally throbbing city where officials are anxious to ensure nothing taints his high-profile visit or the festivities.

The Liaoning will participate in activities marking the 20th anniversary of China's People's Liberation Army (PLA) entering the city, defence ministry spokesman Wu Qian told reporters.

The PLA has a garrison in central Hong Kong and is responsible for defending the city, but only recruits mainland Chinese citizens.

Hong Kong does not have its own separate army.

After the handover in 1997 some feared the PLA would be heavy-handed, given the army's crackdown on student protesters in Beijing's Tiananmen Square in 1989.

Instead they have maintained a very low profile and are barred from interfering in local affairs.

The Liaoning left the Chinese city of Qingdao on Sunday, the official Xinhua news agency reported earlier.