Hong Kong democracy activists donned Halloween masks lampooning the city's pro-Beijing leaders on Thursday, defying an emergency law that bans face coverings and sparking renewed clashes with police.

Tear gas was fired in multiple locations Thursday evening, including near a popular nightclub district where thousands of protesters had gatecrashed Halloween celebrations.

Hong Kong's protesters have worn masks to make it harder for police to identify them
Hong Kong's protesters have worn masks to make it harder for police to identify them AFP / Anthony WALLACE

Online forums used to organise the largely leaderless movement encouraged supporters to use a night when revellers traditionally embrace costumes to mock a recently enacted ban on face masks at protests.

Flashmob rallies broke out in multiple locations, hours after the city announced it has plunged into a technical recession for the first time since the global financial crisis over a decade ago.

Police set up checkpoints around Lan Kwai Fong, a tightly-packed entertainment district that hosts a large annual Halloween party, as protesters descended on the area.

Policemen stopped some mask-wearing Halloween revellers from entering the Lan Kwai Fong entertainment area in Hong Kong
Policemen stopped some mask-wearing Halloween revellers from entering the Lan Kwai Fong entertainment area in Hong Kong AFP / Anthony WALLACE

Many mocked the officers, shouting sarcastic chants such as "I want to drink alcohol and get laid", as well as more familiar protest slogans, as small groups of confused revellers looked on.

Police declared an "unlawful assembly" and eventually fired tear gas to disperse the crowds sending plumes of acrid smoke wafting through the city's commercial district once more.

A masked Halloween reveller flashes a phone message to police in the Lan Kwai Fong entertainment area of Hong Kong
A masked Halloween reveller flashes a phone message to police in the Lan Kwai Fong entertainment area of Hong Kong AFP / Anthony WALLACE

Many of those protesting wore outfits poking fun at the city's leadership.

Yan Lee, an accountant in her 50s, wore a mask that combined the face of justice secretary Theresa Cheng with the Disney villain Maleficent.

"For months she has done nothing for Hong Kong but defend the authorities," she told AFP.

Police stopped Halloween revellers at a popular entertainment area as protesters donned masks lampooning the city's pro-Beijing leaders in defiance of a ban on face coverings
Police stopped Halloween revellers at a popular entertainment area as protesters donned masks lampooning the city's pro-Beijing leaders in defiance of a ban on face coverings AFP / Anthony WALLACE

Another protester, who gave her surname as Loo, had painted her face in the style of Batman's nemesis, The Joker.

She said she was inspired by the recent Hollywood film that traces The Joker's origin story as he launches a revolution against Gotham City's elites.

Protesters faced off against police in the Lan Kwai Fong area
Protesters faced off against police in the Lan Kwai Fong area AFP / Anthony WALLACE

"The idea that everyone owns the spirit to fight touched me a lot," she said.

Tear gas was also fired across the harbour in Mongkok and Prince Edward where hardcore protesters had adopted a less satirical but more familiar tactic -- blocking roads and setting fire to makeshift barricades.

Activists were marking two months since police were filmed beating protesters in Prince Edward subway station, one of multiple incidents this summer that have fanned hostility towards the force.

AFPTV / Vivian LIN, Ayaka MCGILL

Legal challenge to mask ban

Hong Kong has been upended by nearly five months of huge, often violent, pro-democracy protests in which participants routinely wear masks to hide their identities and protect themselves from teargas and pepper spray.

Earlier this month city leader Carrie Lam invoked colonial-era legislation for the first time in more than fifty years to outlaw face coverings at rallies.

The move was seen as a watershed legal moment for the city since its 1997 return by Britain to China -- but the ban has done little to stop the protests or dissuade people from wearing masks.

Earlier on Thursday, activists went to court to challenge the emergency law.

"This is a duel between the rule of law and totalitarianism," lawmaker Dennis Kwok told reporters outside the High Court at the start of a two-day hearing.

The sweeping 1922 emergency law was passed by then colonial master Britain to deal with striking workers and allows the city's leader to make "any regulations whatsoever" in a time of emergency or public danger.

It was last used in 1967 by the British to help suppress Maoist-backed leftist riots that raged for nearly a year and killed some 50 people.

Lam's use of the law was controversial because it bypassed the Legislative Council, the partially-elected chamber that approves Hong Kong's laws.

Critics said the move undermined the city's reputation for being a dependable business and legal hub at a time of growing concern over Beijing's control of the city.

Reputation hammered

The protests were initially sparked by a now-abandoned plan to allow extraditions to the authoritarian mainland. But they snowballed into a wider democracy and police accountability movement.

Violent clashes have broken out between hardcore protesters throwing petrol bombs and bricks at police who are responding with ever increasing amounts of tear gas and rubber bullets.

The clashes have hammered the city's once-solid reputation for stability and have further battered an economy that was already reeling from the US-China trade war.

Lam and Beijing have shown little appetite to meet protester demands, or to offer a political solution.

On Thursday evening China's Communist Party elite concluded a key meeting in Beijing with a promise to protect the "stability" of Hong Kong without giving concrete details.