HONG KONG: Prominent Hong Kong democracy activists including a lawmaker were arrested Friday in a protest crackdown -- a move described by rights groups as a well-worn tactic deployed by China to suffocate dissent ahead of key political events.

The sweep comes after a major rally planned for Saturday was banned by police on security grounds, and then called off by the organisers.

The latest protest had been due to mark the fifth anniversary of Beijing's rejection of a call for universal suffrage in the semi-autonomous city, sparking the 79-day Umbrella Movement in 2014.

Hong Kong has been locked in three months of political crisis, with increasingly violent clashes between police and protesters that have prompted an escalating intimidation campaign from China.

Two of the Umbrella Movement's leaders, Joshua Wong and Agnes Chow -- both still well-regarded among the city's youth -- appeared in court accused of "inciting others to take part in unauthorised assembly" among other charges, having been arrested in dawn swoops on Friday.

After receiving bail, they spoke outside the court and Wong vowed to "continue our fight", railing against the "chilling effect" of the arrests on opponents of Hong Kong's Beijing-backed government.

Authorities are "trying to create white terror" to scare people away from participating in the social and democratic movement, he added -- deploying a term used for China's efforts to fragment and harass the protesters.

The European Union's diplomatic chief Federica Mogherini on Friday said the developments were "extremely worrying".

The day saw rolling arrests of leading pro-democracy voices, including lawmaker Cheng Chung-tai, who advocates greater political autonomy for Hong Kong, his Civic Passion party said in a Facebook post.

Police confirmed that a 35-year-old man surnamed Cheng had been held over "conspiracy to cause criminal damage" linked to the storming of the city's parliament in July.

Pro-democracy campaigner Rick Hui -- a district councillor -- and former student leader Althea Suen were also arrested separately, while vocal independence campaigner Andy Chan was detained at Hong Kong's airport.

More than 900 people have been arrested in connection with protests since June.

But that has failed to snuff out a leaderless movement, which says freedoms in the city, unique within China, are being eviscerated by Beijing.

Amnesty International decried Friday's "ludicrous dawn swoops", describing them as "scare tactics straight out of Beijing's playbook".

Police spokesperson John Tse denied the slew of arrests were timed specifically to defang the weekend's protests as "totally false."

- Defy the ban? -

Hong Kong's crisis-hit government has refused to back down over the protests, which have by turns seen millions march, closed the airport and left city streets strewn with bricks and shrouded in tear gas.

What started as a pushback against a bill allowing extraditions to mainland China quickly morphed into wider calls for democracy and police accountability.

Bonnie Leung of the Civil Human Rights Front (CHRF), the organiser of Saturday's banned rally, said it had "no option but to cancel the march".

However, pockets of protesters have vowed to hold creative events at the scheduled time and place to sidestep the ban.

Those included a mass shopping trip, football match and impromptu religious gatherings in downtown Hong Kong, while a YouTuber with 800,000 followers called a fan meeting.

With a hardcore minority among the protesters, mainly young students, unlikely to heed the police ban, the weekend could be poised for renewed violent clashes.

Student protester Kelly, who wanted to be identified only by her first name, said the arrests would not cow the movement.

"The police think there are leaders behind the protests and this will stop us," she said.

"We are our own leaders and we will keep coming out."

On Sunday, the city saw some of its worst clashes, with running battles between a core group of radical protesters, armed with bricks and Molotov cocktails, and police wielding batons, rubber bullets and tear gas.

One officer fired a warning shot -- believed to be the first live round used during the protests -- as a mob with sticks set upon several policemen.

The violence has damaged Hong Kong's reputation for stability and prosperity.

China has responded with a campaign of intimidation and state-media on Friday reported that fresh military anti-riot drills were held across the border in Shenzhen.

Businesses in the financial hub -- from airline Cathay Pacific to the city's metro operator -- have also been squeezed by Beijing for harbouring apparent supporters of the pro-democracy movement.

Cathay sacked several staff over the protests and on Friday the airline went further, threatening to sack any staff who join a scheduled two-day strike next week.