An outpouring of grief swept Hong Kong on Saturday as crowds paid their respects and laid flowers for the 128 people killed in one of the city's deadliest fires, marking the start of an official, three-day mourning period.

A huge fire still burning in a Hong Kong high-rise apartment complex that has killed at least 55 people with almost 300 missing poses the biggest test of Beijing's grip on the city it has transformed since the mass pro-democracy protests of 2019.

China has cemented its position as a global leader in artificial intelligence, while Hong Kong is carving out a niche as a specialised innovation hub, underpinned by the country's strong governance and regulatory competitiveness,