Beijing held a flag ceremony to mark the 25th anniversary of Hong Kong's handover to Chinese rule as the former British colony swears in a new leader.

The Chinese capital bustled with soldiers during the daily rites in Tiananmen Square on July 1.

The red Chinese fluttered high as troops marched in formation around the square - the site of a brutal massacre that killed thousands of demonstrators calling for political and economic reform in 1989.

The festivities come during the oathtaking of Hong Kong's new hardline pro-Beijing chief executive John Lee.

The city's former security head, Lee rose to power after being chosen by a committee said to be composed of Beijing loyalists. Chinese President Xi Jinping personally oversaw his oath-taking ceremony.

The United Kingdom handed over its former colony Hong Kong to Chinese rule in July 1, 1997. Under the agreement, China promised to give Hong Kong 'a high degree of autonomy, except in foreign and defence affairs' in a set-up called 'one country, two systems.'

However, critics say Communist China is tightening its grip on Hong Kong following the city's passage of a draconian national security law in 2019, allegedly weaponised to silence pro-democracy activists.