Hong Kong's leader Carrie Lam was forced into a rare apology on Sunday after hundreds of thousands of protesters, dressed in black and carrying white flowers as a sign of mourning, poured onto the streets demanding she scrap a controversial extradition law and resign.

Organisers claimed numbers were double the estimated one million who turned out last week and the protest route closed major trunk roads deep into the night.

It was an extraordinary show of people power in a city whose freedoms are being increasingly squeezed by Beijing, and ended any hopes that an embattled Ms Lam may have harboured of bringing a swift end to the spiralling political crisis that has engulfed Hong Kong for months.

Protesters refused to be appeased by her unexpected U-turn on Saturday to delay the divisive extradition law, which critics say puts foreign and Hong Kong residents at risk of being swept into China’s opaque justice system and damages the city’s reputation as a safe financial hub.

Instead the crowd chanted “Carrie Lam Step Down!” in unison as it snaked for some two miles between Victoria Park and the Legislative Council. Spurred on by activists’ loudspeakers, they switched between spontaneous cheers, protest songs and shouts of “withdraw, withdraw” in reference to the law.