Activist Joshua Wong, who has become the face of Hong Kong's push for full democracy, walked free from prison on Monday and vowed to join a mass protest movement demanding that the city's Beijing-backed leader, Carrie Lam, steps down.

His release comes as a political crisis in the Chinese-ruled city enters its second week, amid growing uncertainty over the fate of Lam and an extradition bill she postponed at the weekend after it triggered one of the most violent protests in decades.

"I will join to fight against this evil law," said Wong, 22, one of the leaders of the 2014 "Umbrella" pro-democracy protests that blocked major roads in Hong Kong for 79 days.