HONG KONG — 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, step 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 a controversial extradition bill she postponed over the weekend.

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

"I believe this is the time for her, Carrie Lam the liar, to step down."

Wong acknowledged he still had to fully grasp the scale of the crisis at a time when Chinese President Xi Jinping is grappling with a deepening U.S. trade war, an ebbing economy and regional strategic tension.

Protest organizers said almost 2 million people turned out Sunday to demand that Lam resign, in what is becoming the most significant challenge to China's relationship with the territory since it was handed back by Britain 22 years ago.

The mass rally forced Lam to apologize late Sunday over her plans to push through the extradition bill that would allow people to be sent to mainland China to face trial.

Even after her apology, Hong Kong opposition politicians are echoing marchers' calls for both Lam and the law to go.

"Her government cannot be an effective government, and will have much, much, much difficulties to carry on," veteran Democratic Party legislator James To told government-funded broadcaster RTHK.

"I believe the central people's government will accept her resignation."

However, the official China Daily said Beijing's leaders would continue to back Lam, as it lashed out at foreign "meddling" in the crisis.

China's support for Lam will "not waver, not in the face of street violence nor the ill-intentioned interventions of foreign governments," the newspaper said in an editorial.

While Lam delayed the bill, it has yet to be completely shelved, despite domestic and international fears that it could imperil the status of Hong Kong as a financial hub.

"We cannot accept her apology, it doesn't remove all our threats," said social worker Brian Chau, one of several hundred protesters who stayed overnight in the Admiralty district around the government headquarters and legislature.

Some demonstrators cleared rubbish left after the vast, but peaceful, march while others sang "Hallelujah," a gospel song that has become a feature of the protests against Lam.

The headquarters will stay closed on Monday, the government said. Standing by were a smattering of uniformed police without riot gear, in contrast to their appearance during recent skirmishes with protesters.