Hundreds of thousands of protesters 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."
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.
More than 800,000 people participated in the march, according to organizers the Civil Human Rights Front (CHRF), in what appeared to be a resounding show of support for the movement after six months of occasionally violent unrest. The police put the figure at 183,000.
The mostly peaceful event marked the first time since mid-August that a march organized by the CHRF had been granted police approval. The group was responsible for two back-to-back weekend marches in early June, which it estimates drew a combined total of more than 3 million people.
Protests 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.
Many of those in attendance Sunday 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.
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.
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.
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.
CNN's Eric Cheung and Rebecca Wright contributed to this report.