PROTESTERS walk past a Christmas tree (back) as they march through the Harbour City shopping mall in the Tsim Sha Tsui district of Hong Kong. AFP

Hong Kong marked Christmas Eve with tear gas and mall clashes on Tuesday night as battles between democracy activists and riot police swept through a major shopping district.

The evening’s unrest was the most sustained in what has otherwise been a few weeks of comparative calm for a city upended by more than six months of violent protests.

Thousands of black-clad protesters — some wearing Santa hats and reindeer antlers — took to the streets of Tsim Sha Tsui, a usually bustling tourist district.

Clashes soon erupted with riot police firing multiple rounds of tear gas to disperse protesters throughout the evening, including outside the famous Peninsula Hotel.

Police said a “large group of rioters” had built barricades, damaged traffic lights and dug up bricks on the area’s major thoroughfares.

Meanwhile, flashmob rallies were held in multiple malls across the financial hub, with protesters chanting anti-government slogans.

In Harbour City, a luxury mall, police used pepper spray and batons when a group of plainclothes officers were discovered and surrounded, an AFP reporter on the scene said.

The plainclothes officers made multiple arrests as the crowds threw objects and heckled them.

Riot police quickly arrived at the scene, one aiming a shotgun at protesters as shops quickly shuttered.

Flashmob rallies formed in at least four other locations on Tuesday night with riot police trying to disperse crowds shouting chants and heckling officers.

Footage posted on social media from a mall in Yuen Long district showed a man barging into a police officer and leaping one storey below in a bid to avoid arrest.

In a statement, police said officers were responding to reports protesters were vandalising shops in the mall and that the man who fell was taken to hospital in a conscious state and arrested for assault.

Hong Kong’s many malls have become regular protest venues as protesters try to cause economic disruption in their push for greater democratic freedoms and police accountability.

Online forums have called for pop-up demonstrations over the Christmas and New Year period targeting shopping districts.

A former British colony with a sizeable Christian population, Hong Kong is having a distinctly muted Christmas this year.

Swathes of the population are seething against Beijing’s rule and the semi-autonomous city’s local government.

The months of protest have helped tipped a financial hub already battered by the trade war into recession and sparked intense political polarisation.

Christmas Eve is usually a major night for retailers and bars, with key districts pedestrianised.

But police said they would not close roads to traffic this year fearing protesters might use the opportunity to gather.

Hong Kong’s protests were initially sparked by a now-abandoned attempt to allow extraditions to the authoritarian mainland.

They have since morphed into a popular revolt against Beijing’s rule, with spiralling fears that the city is losing some of its unique liberties.

Local leader Carrie Lam eventually scrapped the extradition bill but both she and Beijing have refused any further concessions.