Hong Kong (AFP) - The jailing of Hong Kong's best-known democracy activists has pushed a new wave of young leaders to take the helm as they seek to keep the movement's message alive.

Joshua Wong and Nathan Law, who carved out international reputations with their campaigning, were both sent to prison last month in what rights groups slammed as politically motivated prosecutions.

Alongside fellow activist Alex Chow, they are serving sentences of between six and eight months for their roles in a protest that triggered mass Umbrella Movement rallies in 2014 calling for democratic reforms.

The jailings were a blow to the pro-democracy movement and seen as more evidence that Beijing is tightening its grip on semi-autonomous Hong Kong.

But they also breathed new life into a campaign that had been struggling for momentum since the 2014 rallies failed to win concessions.

Tens of thousands took to the streets to protest the jail terms last month, and activists who have long been at the right hand of Wong and Law are now stepping into the spotlight.

"We should try to do more, not only for them but also for our city and to show the government and the Chinese regime that we are not going to be scared," Agnes Chow, 20, a close friend of the jailed activists, told AFP.

Chow addressed the crowds at last month's protest over the sentences and has regularly spoken to the media since her friends were imprisoned.

If a by-election for the Hong Kong legislature is held early next year -- after her 21st birthday in December -- she would be old enough to run for Law's vacated seat, and has not ruled that out.

Law was one of four pro-democracy lawmakers disqualified from parliament in July for inserting protests into their oaths of office.

Chow is already a seasoned activist -- she was one of the core members of Wong's Scholarism group, which organised huge rallies in 2012 forcing the government to shelve a proposal to introduce compulsory patriotic "national education" into schools.

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She was also one of the best-known faces of the Umbrella Movement, regularly taking to the stage to address protesters, and is a member of Wong and Law's political party Demosisto.

Chow said the government was using the jail terms to scare people away from social movements.

"It is important for us to learn how to overcome fear in order to fight for our own basic human rights and freedom and democracy," she said.

- Turning point -

Chow and fellow Demosisto member Derek Lam said the democratic movement now needed to improve its connections at the grassroots level to build a stronger base.

Lam, 24, who made an emotive speech outside the jail where Chow and Law are being held and is one of Demosisto's most recognisable leaders, said the party ranks had swelled in the past two months.

"Young people are all trying to find a way to change Hong Kong," he added.

But Lam also faces charges over an anti-China demonstration last year and believes there will soon "only be a few people left" to lead the cause.

Activist Lester Shum said those who are free to continue campaigning should put pessimism aside.

Shum, 24, also a prominent student leader during the Umbrella Movement, has been at the forefront of recent protests over the jailings.

He said the imprisonment of Wong, Law and Chow was a turning point for the democratic movement.

"They have been facing their situation with a very calm and determined attitude," he told AFP.

"I think this will somehow encourage pro-democratic Hong Kong people," said Shum, who is assistant to popular pro-democracy lawmaker Eddie Chu.

Shum is facing contempt of court charges relating to the clearance of one of the Umbrella Movement protest sites. Visibly thinner than when he first came on the scene, he said there had been an emotional toll.

"One of the worst things for me has already happened," he said, referring to the imprisonment of his girlfriend Willis Ho.

She was one of 13 activists recently jailed for charging the Legislative Council building in 2014 in protest over re-development plans for rural areas.

But he remains optimistic about the city's campaign for democracy and vowed to fight on.

"If we could stand up against their agenda, stand up against the challenges given to us by them, I think Hong Kong people will not be defeated easily."