Masked assailants attack Hong Kong protesters in subway station after demonstration

Tania Snuggs, news reporter

Clashes in Hong Kong escalated into violence on Sunday as police launched tear gas at pro-democracy protesters and a group of masked assailants attacked people making their way back from the rally in a subway station.

The firing of tear gas was the latest confrontation between police and protesters who have taken to the streets for almost two months to fight a proposed extradition bill and call for electoral reforms in the Chinese territory.

Hours after the largely peaceful rally, officers waved a black warning flag before throwing gas canisters at campaigners after they refused to leave the area.

Organisers of Sunday's rally, calling for an independent investigation into police tactics used during earlier demonstrations, say about 430,000 people took part.

Many ignored the designated end point in the Wan Chai district and continued on to China's central government building, where the country's national emblem was defaced with black ink.

Protesters threw eggs at the liaison office and spray-painted surrounding surveillance cameras.

Later, anti-government protesters leaving the march filmed a series of attacks on them by what appeared to be pro-Beijing gangs inside a subway station in the city's Yuen Long district.

Video footage on social media shows a group wearing white t-shirts with black masks pulled over their heads, hitting people - including pro-democracy demonstrators clad in their trademark black clothing - with sticks and umbrellas.

The South China Morning Post reported that at least 36 people were injured, but no official figures have been released.

At a counter-rally earlier in the day, campaigners wore white in support of police, who some metro passengers accused of not intervening in the attack.

In a statement released shortly after midnight, the Hong Kong government said commuters had been assaulted, leading to "confrontations and injuries".

It added that "some radical protesters initiated a series of violent acts, despite repeated warnings" by the police.

The acts were said to include the hurling of petrol bombs, setting fires and throwing bricks.

The statement continued: "This is absolutely unacceptable to Hong Kong as a society that observes the rule of law."

On Friday, Hong Kong police found a stash of a powerful homemade explosives and arrested a man in a raid on a commercial building.

Media reports claimed materials voicing opposition to the extradition bill were found at the site, but a police spokesman said no concrete link had been established and that the investigation was continuing.

Mass demonstrations began last month in opposition to a contentious extradition bill that would have allowed Hong Kong residents to stand trial in mainland China.

Hong Kong - a former British colony returned to Chinese rule in 1997 - has been promised certain freedoms under a "one country, two systems" framework.

Hong Kong leader Carrie Lam has declared the bill dead, but some protesters are also calling for her to resign amid growing concerns about the steady erosion of civil rights.

The demonstrations have since escalated into calls for democratic reforms and an investigation into alleged police brutality.