HONG KONG — Around 400 protesters were arrested after a police-approved march attended by tens of thousands on New Year's Day escalated into violence, authorities said.

The arrests, which police said were for unlawful assembly and possession of offensive weapons, came after officers fired several rounds of tear gas, as anti-government protests in the semi-autonomous city continued into the new year.

Hong Kong broadcaster RTHK showed pepper spray and tear gas being deployed against demonstrators in the busy commercial district of Wan Chai Wednesday afternoon as protesters marched from the city’s Victoria Park and into the central business district.

Hong Kong police said in a statement that some protesters started hurling Molotov cocktails as well as vandalizing multiple banks and shops along the route of a public procession, which forced them to prematurely end the march and tell the crowds to disperse.

But in a further escalation Wednesday evening, some protesters dug in, barricading roads, starting fires and pointed lasers at officers, prompting police to deploy a water cannon and fire more tear gas.

Earlier in the day, citizens young and old marched in a largely peaceful rally, carrying signs that read “five demands, hold on till the end” and “never give up." Many were wearing face masks to conceal their identities.

“Hong Kong needs its freedom. It’s one country, two systems - not one country, one system,” said Sandy Lo, a housewife who came to the march with her young son, referring to the unique model that governs the former British territory and guarantees freedoms not granted in mainland China. “We hope that [Hong Kong leader] Carrie Lam listens to our voice.”

Several protesters were carrying American flags and told NBC News they were grateful for President Donald Trump’s backing of legislation supporting human rights in Hong Kong — a move that enraged Beijing.

“We deeply appreciate it and are deeply grateful for his support,” sales manager Claudia Chin, 26, told NBC News. “We are here to thank him.”

Wearing big sunglasses and a face mask, she added that she hoped 2020 will be the year protesters get their five demands, including universal suffrage.

For months, demonstrators have been pushing for concessions from the government, including full democracy, an amnesty for protesters who have been arrested so far and an independent investigation into police actions.

“This is the year that we really hope these demands will come true," Chin said.

Hong Kong toned down its New Year's Eve celebrations amid the protests that have dragged on since June.

The months-long civil unrest was sparked by a controversial bill that would have allowed residents to be extradited to China. Although the bill has been shelved, the demonstrations have transformed into a wider movement against the erosion of the former British colony's civil liberties promised after the city was handed over to China in 1997.

Beijing has denied claims that it’s interfering in Hong Kong's affairs, blaming the west for fomenting the unrest.

A recent poll conducted for Reuters by the Hong Kong Public Opinion Research Institute showed that the protest movement is supported by 59 percent of city residents, with more than a third of respondents saying they had attended an anti-government demonstration.

However, protests have grown increasingly violent in recent months, impacting Hong Kong's reputation as a financial capital and tourism hot spot.

In her New Year's address, Hong Kong leader Carrie Lam said the months of protests had brought “sadness, anxiety, disappointment and even rage," and she vowed to tackle underlying social and economic problems in the coming year.

Lam said she would “listen humbly" to help bring an end to the protests.

On Wednesday, lawmakers and civic leaders from 18 countries urged Lam to set up an independent probe into police’s use of force in the protests, warning they would otherwise call for an inquiry at the international level, South China Morning Post reported.

Meanwhile, Chinese President Xi Jinping said in comments broadcast on Tuesday that he "sincerely wishes Hong Kong and our Hong Kong compatriots well,” adding the situation there has been of a concern.

"Without a harmonious and stable environment, how can people live in peace and enjoy their work?" Xi said in a New Year's Eve speech carried on state television. “Hong Kong’s prosperity and stability is the wish of Hong Kong’s compatriots and it’s also the expectation of the people our motherland,” he added.

Mark Roberts and Veta Chan reported from Hong Kong, Yuliya Talmazan from London.