The territory has seen tumultuous times since July 1, 1997, with economic turmoil, outbreaks of disease and more recently, pro-democracy protests casting shadows over the island, its stunning harbour and the New Territories up to the border with mainland China.

Hong Kong's reputation as a free-market haven was challenged during the 1997-98 Asian financial crisis, while the 2008 global financial crisis tested the health of its banks.

The city of 7.3 million people suffered badly during an outbreak of severe acute respiratory syndrome, or SARS as it is known, in 2003, when 299 people died from the flu-like virus. It was also among the places hardest hit by bird flu.

A rush of money from mainland China vaulted Hong Kong into the ranks of the world's most expensive property markets. It also fuelled public anger over high living costs and a widening wealth gap.     

"My priority will be to heal the divide and to ease the frustration – and to unite our society to move forward," Chief Executive-elect Carrie Lam said in March after her selection by a 1,200-person election committee stacked with Beijing and pro-establishment loyalists.

From 1997 to 2017: Hong Kong in pictures  

Chinese President Xi Jinping is due to attend anniversary events on the island this week, including Lam's swearing into office on Saturday as the city's first female leader.

Lam, 60, is the territory's fourth leader since it reverted to Chinese rule on July 1, 1997.

As part of the handover, a mini-constitution known as the Basic Law promised that Hong Kong would retain a high degree of autonomy under a "one country, two systems" formula, with full democracy an "ultimate aim".

But two decades later, there's no sign of that.

China declined to make any concessions to student protesters demanding universal suffrage in "Occupy" street demonstrations in 2014.