China's President Xi Jinping arrived in Hong Kong to mark 20 years since the territory was handed back to China by the UK.

As Reuters reported, parts of Hong Kong are under a tight security lockdown amid worries of further protests, with several major roads closed and sections of the city centre blocked off from the public, in connection with the visit of Xi Jinping.

The UK returned Hong Kong to Chinese rule in 1997 under a "one country, two systems" formula which guarantees wide-ranging autonomy and judicial independence not seen in mainland China. 

Tensions between Hong Kong and China have intensified amid concern and resentment over Beijing's growing interference in the former British colony.