Hong Kong student leader Alex Chow on Sunday accused police of mounting a campaign of harassment against pro-democracy campaigners after he became the latest figure to be arrested and released by police.

Several protest leaders have been summoned in recent days over offences relating to the mass protests that shut down parts of the city late last year, only to be released in what lawyers have condemned as a potential abuse of process.

Police have vowed to investigate the "principal instigators" of the rallies calling for free leadership elections, in what campaigners say is part of a crackdown on the pro-democracy movement.

Chow, who voluntarily turned himself in on Sunday in line with a police request, said he had been formally arrested but not charged after being questioned for around an hour.

"If they have enough evidence, for sure... they can lay the charges," Chow said, accusing the authorities of creating politically motivated "white terror".

"I can't think of any other reason (for the arrests) other than creating white terror or a politically motivated one," he said.

A police spokeswoman declined to comment on Chow's case when asked by AFP.

On Friday, Joshua Wong, the teenage face of the pro-democracy movement, and several other protesters were also arrested on counts relating to the mass protests and then released.

Wong's lawyer Michael Vidler said authorities were trying to create a "sense of uncertainty" and that if charges were laid at a later time based on evidence already in hand it would constitute an "an abuse of process".

Beijing has pledged that Hong Kong can choose its own leader for the first time in 2017 but insists on vetting candidates, an arrangement which protesters dismiss as "fake democracy".

Hong Kong and Beijing have consistently branded the protests illegal.

Other leading figures have been asked to show up at police stations in the week ahead, including outspoken media tycoon Jimmy Lai -- whose house and office were firebombed on Monday -- and the three founders of the Occupy Central campaign.

Hong Kong student leaders arrested, released without charge
Hong Kong (AFP) Jan 16, 2015 - Hong Kong student leaders including the teenage face of the pro-democracy movement, Joshua Wong, were arrested Friday on charges relating to mass protests as authorities target prominent figures who spearheaded the rallies.

Police have vowed to investigate the "principal instigators" of protests for fully free leadership elections that lasted for more than two months and brought parts of the city to a standstill before rally camps were cleared in December.

"I was held for three hours and I was arrested on charges of calling for, inciting and participating in an unauthorised assembly," Wong, 18, said as he emerged from police headquarters to cheering supporters.

Wong had voluntarily turned himself in along with three other student leaders after being requested to do so by police as part of the investigation into the protests. He was formally arrested and questioned, but was released without charge, his lawyer confirmed.

Wong said that police had told him that the investigation was still ongoing so "there is still a chance for prosecution".

But the lawyer representing Wong said that it would be "an abuse of process" for police to try to charge him at a later date based on evidence they already have.

"If they had the evidence to charge they should have charged, that's our view," Michael Vidler told AFP.

"They're seeking to maintain they reserve the right to charge him at a later date, (but) it would be an abuse of process if they were to later charge using exactly the same evidence that they have today.

"It engenders a sense of uncertainty and they are using that, in my view, as a method of control."

Wong said it was a "waste of time" adding that he had been shown media reports and YouTube footage of the protests as part of the interview.

The three other student leaders from the Scholarism campaign group, led by Wong, were also arrested on similar counts relating to the protests and were released without charge, police confirmed.

Supporters applauded Wong shouting "Well done!" as he emerged from the police building.

Wong was the last of the four leaders to meet with police and came out alone.

- 'More students will protest' -

"The police arrests will just motivate more secondary school or university students to come to the streets," Wong said earlier before he handed himself in.

Beijing has pledged that Hong Kong can choose its own leader for the first time in 2017 but insists on vetting candidates, which protesters dismiss as "fake democracy".

Hong Kong and Beijing have consistently branded the protests illegal.

Wong already appeared in court last week for a preliminary hearing on possible criminal contempt charges for blocking the police clearance of one of the main protest camps in November. No formal charges have been laid.

In the morning, the students were surrounded by dozens of supporters some carrying yellow umbrellas -- the symbol of the democracy movement.

One held a "Je Suis Charlie" poster -- a slogan that has come to symbolise the fight for freedom of expression after jihadist gunmen stormed the Paris offices of satirical magazine Charlie Hebdo last week, killing 12 people.

This time it was printed over the backdrop of an umbrella.

Other leading figures have been asked to show up at police stations next week, including outspoken media tycoon Jimmy Lai -- whose house and office were firebombed on Monday -- and the three founders of the Occupy Central campaign.

"People were being unrealistic to think there would be some general amnesty," said Simon Young, who is associate dean for Hong Kong University's Faculty of Law.

"It's more a question of what shape this criminal justice response will take. Will it be harsh and punitive or will it be fairly reasonable?"