(CNN) -- The organizers of the large-scale demonstrations which kicked off Hong Kong's months-long protest movement earlier this year returned to the streets again Sunday, in a bid to maintain pressure on the city's government following the success of pro-democracy groups at recent elections.
Tens of thousands of protesters of all ages began assembling at Victoria Park in Causeway Bay at 3 p.m. (2 a.m. ET) under bright blue skies. Many in the crowd could be seen carrying large banners, bearing slogans such as "Free Hong Kong."
Hong Kong's Police Commissioner, Tang Ping-Keung, told reporters in Beijing said that police would use a "decisive response" to deal with violence, but added they would "adopt more lenient and flexible approaches" to other protesters.
By late afternoon, parts of the city had come to a complete standstill, as crowds attempted to move through the main island to Chater Road close to the main financial hub.
The event, which appeared on course to be the biggest of its kind in recent months, marks the first time since mid-August that a march organized by the Civil Human Rights Front (CHRF) has been granted police approval. The group was responsible for two back-to-back, largely peaceful weekend marches in early June, which it estimates drew a combined total of more than 3 million people.
Protests in the semi-autonomous Chinese city were initially sparked by a now-shelved extradition bill that would have allowed people to be sent across the border to face trial in mainland China, but have since expanded to include calls for greater democracy and government accountability.
Sunday's march had been widely viewed as test of the movement's enduring support after six months of occasionally violent unrest -- and many of those in attendance voiced frustration with the government and its perceived unwillingness to make concessions.
"We want our demands to be heard, we want universal suffrage," said one 23-year-old protester, who did not want to be identified. "We want freedom for Hong Kong and for Hong Kong to be managed in a sustainable way," she added.
The organizers had pegged the rally to international Human Rights Day, which falls on December 10 and marks the United Nations' adoption of the Universal Declaration of Human Rights. "Hong Kong's human rights violations and humanitarian crisis are reaching the tipping point now," CHRF said in a statement, calling on the city's government to "uphold its commitment to Universal Declaration of Human Rights and all UN human rights treaties applicable to Hong Kong."
Organizers have vowed to keep the protest peaceful, and had reportedly deployed 200 marshals to handle any potential conflicts between marchers and the police.
Elsewhere on Sunday, the government of Hong Kong criticized an arson attack at the Court of Final Appeal, where a small fire was set outside the entrance. They said in a statement that the incident "not only disrupted social peace but also undermined Hong Kong's reputation as a city governed by the rule of law."
The police have permitted the CHRF to hold rallies in recent months, but not march, and several unauthorized demonstrations have broken out into violent conflicts between protesters and police.
"This is the last chance given by the people to (Chief Executive) Carrie Lam," CHRF convenor Jimmy Sham said Friday, according to AFP.
The group has called on Lam, the city's leader, to meet the protest movement's demands, including an independent investigation into allegations of police brutality and the restarting of political reform to allow full universal suffrage for how the city's leader and legislature are chosen.
There has been something of a lull in protests since pro-democracy candidates scored a landslide victory in local council elections last month, but frustration is growing at Lam's failure to respond to those results in any meaningful way.
Protesters celebrated the passage of the Hong Kong Human Rights and Democracy Act in the United States, cheering what some described as US President Donald Trump's "thanksgiving present" to them, but any gift from their own government, or the authorities in Beijing, does not seem forthcoming.
The high turnout for Sunday's march is likely to reiterate the message of support for the protest movement delivered by the election results, and add pressure on Lam to come up with some kind of compromise solution.
In a statement, the city's government said it "hopes that members of the public, when expressing their views and opinions as well as striving for their own rights and freedom, can embody the tenets of the Universal Declaration of Human Rights to respect others' rights and freedom. All violent and illegal acts are contrary to the spirit of the Declaration."
"From June this year until now, there have been over 900 public demonstrations, processions and public meetings," the statement added. "Unfortunately, many ended in violent and illegal confrontations, including reckless blocking of roadways, throwing petrol bombs and bricks, arson, vandalism, setting ablaze individual stores and facilities of the Mass Transit Railway and Light Rail, and beating people holding different views."
The statement said that the government was willing to "engage in dialogues, premised on the legal basis and under a peaceful atmosphere with mutual trust," and added that in the wake of the extradition bill crisis which kicked off the protests, it has "learned its lesson and will humbly listen to and accept criticism."
On Sunday, police said they had seized a "large amount of weapons, including one firearm and over a hundred bullets" during raids that morning. Eight men and three women were arrested in connection with the operation, they said in a statement.