Thousands of Hong Kong revelers welcomed in 2020 on neon-lit promenades along the picturesque Victoria Harbour, breaking into pro-democracy chants as the clocks struck midnight after more than half a year of often violent unrest.

Protesters briefly blocked Nathan Road, a key artery leading through Kowloon to the harbour, after forming human chains across the Chinese-ruled city and marching through shopping malls, urging people not to give up the fight for democracy in 2020.

The protesters fled when police came to clear the road of umbrellas, street furniture and debris and a three-meter-tall skeleton of a metal Christmas tree. Several arrests were made.

Authorities had cancelled the popular new year fireworks for the first time in a decade, citing security concerns. A "Symphony of Lights" took place instead, involving projections on the city's tallest skyscrapers after the countdown to midnight.

There were small-scale pyrotechnics on waterfront rooftops, but the grandiose fireworks launched from vessels in the centre of the harbour, broadcast around the world every year, were absent.

A man is detained by riot police outside of a police station at Mongkok district on New Year's Eve in Hong Kong. (Anthony Kwan/Getty Images)

The carnival atmosphere on the harbour was interrupted as parts of the crowd of thousands watching the show began chanting protest slogans, such as "Liberate Hong Kong! Revolution of our times" and "Five demands, not one less."

The latter refers to the goals of the anti-government movement, which include universal suffrage and an independent inquiry into alleged police brutality.

The protesters are angry at what they see as creeping Beijing influence in the city which was guaranteed wide-ranging autonomy when it returned from British to Chinese rule in 1997. Beijing denies interference and blames the West for fomenting the unrest.

"I hope people can continue fighting in 2020," 28-year-old engineer Eric Wong said.

"We should not forget the people in jail who could not count down to the new year with us."

Carrie Lam hopes to 'begin again, together' in 2020

In a New Year's Eve video message, Chief Executive Carrie Lam said more than six months of unrest in the Asian financial hub had caused sadness, anxiety, disappointment and rage.

"Let's start 2020 with a new resolution, to restore order and harmony in society. So we can begin again, together," said Lam in the three-minute address.

Chinese President Xi Jinping extended his best wishes to Hong Kongers in a speech carried by state television.

"The situation in Hong Kong has been everybody's concern over the past few months," Xi said.

"Without a harmonious and stable environment, how can there be a home where people can live and work happily? We sincerely hope for the best for Hong Kong and Hong Kong compatriots."

Police say they have arrested nearly 6,500 people since the protests began escalating in what is the worst political crisis faced by the city in decades.

On Jan. 1, tens of thousands of people are expected to join a major pro-democracy march, after it received police approval to proceed.

The previous such march by organizers, the Civil Human Rights Front (CHRF), in early December, drew an estimated 800,000 people.

The New Year demonstrations follow a pickup in clashes since Christmas Eve, when riot police fired tear gas at thousands of protesters following scuffles in shopping malls and in a prime tourist district.

"On New Year's Day, we need to show our solidarity … to resist the government. We hope Hong Kong people will come onto the streets for Hong Kong's future," said CHRF leader Jimmy Sham.