A leading figure in Hong Kong's 2014 Umbrella Movement demonstrations has been released from prison, as uncertainty grows over the fate of government leader Carrie Lam and the extradition bill she postponed at the weekend.

Key points: Joshua Wong was jailed over his involvement in 2014 pro-democracy protests

Joshua Wong was jailed over his involvement in 2014 pro-democracy protests The former student leader has vowed to join the latest round of demonstrations

The former student leader has vowed to join the latest round of demonstrations The protesters who remained in the streets have moved on after talks with police

Joshua Wong's release from the Lai Chi Kok Correctional Facility came as student demonstrators and police continued to face off in downtown Hong Kong following a massive protest on Sunday.

Organisers said almost 2 million people turned out to demand that Ms Lam step down, 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.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 32 seconds 32 s The massive protests in Hong Kong on Sunday were praised for being peaceful and orderly, with crowds parting to allow an ambulance through.

Mr Wong, 22, served nearly five weeks of a two-month sentence for contempt related to his involvement in the 2014 protests, which advocated for more democratic elections.

His sentence was reduced from three months because he was only a teenager when he was arrested in 2014.

It is unclear why he was released early.

Hong Kong police announced that they wanted to clear the streets of protesters on Monday morning. ( AP: Vincent Yu )

In February, the young activist won an appeal against a separate conviction and six-month sentence for unlawful assembly and was released after spending more than two months in prison in that case, before being sent back to prison in May.

He vowed to join the latest round of protests, calling the extradition law "evil".

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

Mr Wong said he needed a bit of time but that "no matter what happens, I will join the protest soon".

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The mostly young demonstrators still gathered near the city's government headquarters began moving off the streets on Monday morning after hours of haggling with police.

They were streaming into an outdoor space near the city's legislative chamber that had been closed earlier in the day, allowing police to reopen roads that had been blocked since Sunday's protest.

The latest protests were set off by an extradition bill that would have allowed criminal suspects to be sent to mainland China for trials.

Ms Lam has suspended that legislation, but activists who saw it as undermining legal rights and judicial independence want it scrapped altogether.

Protesters who camped out overnight take a rest along a main road. ( AP: Vincent Yu )

She apologised on Sunday over her plans to push through the extradition bill, but Hong Kong opposition politicians continued to call for Ms Lam's resignation.

"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 state newspaper China Daily said Beijing's leaders would continue to back Ms Lam, lashing out at foreign "meddling" in the crisis.

China's support for Ms 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.

Policemen stand guard on a road as protesters march toward the Legislative Council. ( AP: Vincent Yu )

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