Many of those attending voiced anger that chief executive Carrie Lam and Beijing have ruled out any further concessions despite the landslide election defeat.
"No matter how we express our views, through peacefully marching, through civilised elections, the government won't listen," said a 50-year-old protester, who gave his surname Wong. "It only follows orders from the Chinese Communist Party."
"What has been stirred up in society the past few months won't simply fade away if the government refuses to solve the problem of systematic injustice," added Sirius Tam, 21, who donned a giant mask of Pepe the Frog, a cartoon character who has become an irreverent symbol of the protests.
Semi-autonomous Hong Kong has been battered by increasingly violent demonstrations in the starkest challenge the city has presented to Beijing since its 1997 handover from Britain.
Millions have hit the streets in protests fuelled by years of growing fears that authoritarian China is stamping out the city's liberties.
The last fortnight has seen a marked drop in street battles and protester vandalism after the landslide win by pro-democracy candidates.
Police took the unusual step of allowing the Civil Human Rights Front (CHRF) to hold Sunday's march -- the first time the group has been granted permission since mid-August -- but they warned they would have zero tolerance for violence by radicals.
The movement's demands include an independent inquiry into the police's handling of the protests, an amnesty for those arrested, and fully free elections.
"This is the last chance given by the people to Carrie Lam," CHRF leader Jimmy Sham said.
The protests are largely leaderless and organised online. They were initially sparked by a now-abandoned attempt to allow extraditions to the mainland but have since morphed into a popular revolt against Beijing's rule.
The CHRF, which advocates non-violence, has been the main umbrella group behind record-breaking rallies earlier in the summer that saw huge crowds regularly march in searing heat.
Authorities have repeatedly banned major rallies in recent months citing the risk of violence from hardcore protesters.
Large crowds have simply ignored the bans, sparking near-weekly tear gas and petrol bomb clashes that have upended Hong Kong's reputation for stability and helped tip the city into recession.
But fears of violence remain.
Hours before the march was due to kick off, police displayed weapons, including a pistol and knives, they said had been found during overnight raids where eleven people were arrested.
"We believe the group planned to use the weapons to incite chaos during the march later today and impugn the police," senior superintendent Lee Kwai-Wa, from the city's organised crime bureau, told reporters.
Monday marks the six-month anniversary of the protests during which some 6,000 people have been arrested and hundreds injured, including police.
Online forums used to organise the movement's more radical wing have vowed to target the morning commute on Monday if there is no response from Lam.
Years of huge, peaceful democracy marches have made little headway, leading to increased radicalisation among some Hong Kong protesters and a greater willingness to embrace violent tactics.
But there is little sign Lam is willing to budge, leading to fears the lull in street clashes will be temporary.
Since the local elections the city's chief executive has remained steadfast in her opposition to further concessions and Beijing has stuck by her even as she languishes with record low approval ratings.
The police force's reputation has also taken a hammering.
Police have defended their handling of the protests and say their force has matched rising violence from hardcore protesters.
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