Though the gathering was largely peaceful, violence broke out in some areas and police fired tear gas.

On New Year's Eve, demonstrators had formed human chains that stretched for miles down busy shopping streets.

More than six months after the protests began, they gathered for midnight countdowns by Victoria Harbour.

Their chants included, "Ten! Nine! Liberate Hong Kong, revolution now!"

In the lively Mong Kok market district, some set fire to barricades after dark and let off fireworks, disrupting traffic.

Police used water cannon to clear Nathan Road in Mong Kok and fired tear gas and rubber bullets, the South China Morning Post reports.

Some 40 parliamentarians and dignitaries from 18 countries sent an open letter to Hong Kong's leader Carrie Lam on New Year's Eve, urging her to "seek genuine ways forward out of this crisis by addressing the grievances of Hong Kong people".

The anti-government protests began in June over plans to allow extradition to mainland China, but have since morphed into a broader movement demanding full democracy.

Some protesters have adopted the motto: "Five demands, not one less!"

Their goals are an amnesty for those arrested, an independent inquiry into alleged police brutality, universal suffrage, and for the protests not to be characterised as "riots". The fifth demand - the withdrawal of the controversial extradition bill - has already been met.

Hong Kong was a British colony until 1997, but was then returned to Chinese control under the principle of "one country, two systems". While it is technically part of China, the territory has its own legal system and borders, and rights including freedom of assembly and free speech are protected.

More than 6,500 people have been arrested as a result of the protests so far.

'Freedom is not free'

In the afternoon of New Year's Day, people of all ages gathered to march from the city's Victoria Park. Some wore masks, defying a ban on face coverings, and carried signs reading, "Freedom is not free".

"It's hard to utter 'Happy New Year' because Hong Kong people are not happy," said a man named Tung, according to Reuters news agency. "Unless the five demands are achieved, and police are held accountable for their brutality, then we can't have a real happy new year."

The pro-democracy march was organised by the Civil Human Rights Front (CHRF), which has planned a number of million-strong rallies.

"The government has already started the oppression before the New Year began... whoever is being oppressed, we will stand with them," said Jimmy Sham, a CHRF leader and long-time political activist.

Mr Sham was hospitalised in October after he was attacked by a group of men wielding hammers.

In a speech on New Year's Day, China's President Xi Jinping said Beijing would "resolutely safeguard the prosperity and stability" of Hong Kong.