Chow was released from prison after serving nearly seven months for her role in an unauthorised assembly during anti-government protests in the city in 2019.
Anti-Beijing activist Agnes Chow has been released from a Hong Kong prison on the second anniversary of the city's huge democracy rallies, with police out in force and protests now all but banned.
Two thousand officers have been placed on standby after social media calls for residents to commemorate the failed democracy demonstrations.
Authorities have kept a coronavirus prohibition on public gatherings despite the city recording just three local infections in the last month.
A Beijing-imposed national security has also criminalised much dissent and most of the city's democracy leaders have been arrested, jailed or fled overseas.
On Saturday morning, one of those figures walked free from prison.
Many supporters are waiting for #HongKong pro-democracy activist #AgnesChow in the early morning to give her a warm welcome. Her release also attracts wide international media coverage.— Eileen Chang 😷⛑🥽🌂🧤🇭🇰 (@EileenEChang) June 12, 2021
Video: NineteenthMedia pic.twitter.com/PRbvOdAa4o
Chow, 24, was mobbed by waiting media but made no comment. She wore a t-shirt emblazoned with the phrase "You are doing so great".
Chow hails from a generation of activists who cut their teeth in politics as teenagers and became an inspiration for those who chafe under Beijing's increasingly authoritarian rule.
She spent around seven months behind bars for her role in a 2019 protest outside the city's police headquarters. Fellow youth activists Joshua Wong and Ivan Lam were sentenced in the same case.
Chow's release comes at a sensitive time.
Two years ago on June 12, thousands of protesters surrounded the city's legislature in an attempt to stop the passage of a bill that could have allowed extraditions to mainland China's opaque judicial system.
Riot police used tear gas and rubber bullets to disperse the huge crowds.
Footage of the clashes deepened public anger, and fuelled what became an increasingly violent movement calling for full democracy that raged for seven straight months.
Huge crowds rallied week after week in the most serious challenge to China's rule since Hong Kong's 1997 handover.
Beijing's leaders have dismissed the call for democracy, portraying those who protested as stooges of "foreign forces" trying to undermine China.
They have since overseen a sweeping crackdown that has successfully curbed dissent and radically transformed the once outspoken semi-autonomous city.
The spear tip of that crackdown is the national security law.
More than 100 people have been arrested under the new law, including Chow.
She has not yet been charged but dozens of others have, including jailed pro-democracy media tycoon Jimmy Lai.
Most have been denied bail and they face up to life in jail if convicted.
Protests have been all but illegal for the last year in Hong Kong but anniversary events can focus attention.
On Friday, two activists from Student Politicism, a pro-democracy group, were arrested on suspicion of advertising an unauthorised assembly.
Last week authorities banned an annual candlelight vigil to commemorate victims of Beijing's deadly 1989 Tiananmen Square crackdown.
But many Hong Kongers still quietly signalled defiance by turning on mobile phone lights and lighting candles that evening.
😢😭— Jack (@Jack27688344) December 3, 2020
Whether or not Joshua Wong, Agnes Chow or others are in the paddy wagon.
Still,many people gathered around the car, chanting the names of people they thought were in it & shouting slogans in support of them.#FreeJoshuaWong#FreeIvanLam#FreeAngesChow
Video : Gwyneth's FB pic.twitter.com/CnGxCAR8vc
'Enemies of Hong Kong'
Western nations say China has torn up Hong Kong's "One Country, Two Systems" model -- a pre-handover promise that the city would keep key freedoms and autonomy.
China's leaders say the security law was needed to return stability.
As Chow was being released, Beijing's top envoy in Hong Kong was speaking to hundreds of dignitaries at an event themed around next month's 100th anniversary of the founding of the Chinese Communist Party.
Luo Huining hit out at western media coverage, international criticism and those who "cry for the end of one-party rule" – a popular pro-democracy slogan in Hong Kong.