Hong Kong's Justice Secretary was pushed to the ground in London last night by a mob of pro-democracy activists yelling 'murderer' as they chased her for 300 yards down the street.

Teresa Cheng, who was in the UK to give a speech about successful dispute resolution in the former British colony, was targeted by dozens of protesters in Holborn who mobbed her as she left her car.

Footage of the incident showed Cheng being swamped and screamed at outside the Chartered Institute of Arbitrators in Bloomsbury Square at around 5pm last night before being chased 300 yards into Bury Place.

In the melee she was then pushed to the ground, landing with an audible thump on her arm and was left stricken on the ground clutching her wrist. She was taken to hospital by ambulance for treatment.

The assault is being investigated by Scotland Yard but there have been no arrests.

Hong Kong has been crippled by protests since March with ten dead and more than 1,000 injured in clashes over Beijing's tightening grip on democracy and plans to extradite citizens to China and Taiwan.

The London attack on Cheng - 6,000 miles from the former British colony - is the first time a demonstrator has got close enough to assault a government minister since the violent protests began eight months ago.

Hong Kong Justice Secretary Teresa Cheng tries to get up after falling when protesters surrounded her in London last night

Cheng was allegedly pushed over by pro-democracy demonstrators and suffered 'serious bodily harm' to her hand, Chinese officials have said

She was swamped in Bloomsbury Square and was unable to give a speech on how Hong Kong is dealing with disputes

A Met spokesman said: 'Police are investigating an allegation of assault in Bury Place, WC1 at around 5.05pm on Thursday.

'A woman was taken to hospital by London Ambulance Service suffering an injury to her arm.

'Enquiries are ongoing to establish the full circumstances. There has been no arrest at this stage'.

Chinese and Hong Kong governments called the protagonists a 'violent mob'.

A statement said Cheng suffered 'serious bodily harm' and the Chinese embassy in the UK later said she was pushed and sustained a hand injury.

'(Cheng) was besieged and attacked by dozens of anti-China and pro-independence activists,' the Chinese embassy said in a statement. The incident showed that the 'violent and lawless perpetrators' were now taking their violence abroad, it said.

China has lodged a formal complaint with Britain and urged British authorities to bring the perpetrators to justice.

Hong Kong's leader Carrie Lam also strongly condemned the attack.

The former British colony's government said in a separate statement: 'The secretary denounces all forms of violence and radicalism depriving others' legitimate rights in the pretext of pursuing their political ideals, which would never be in the interest of Hong Kong and any civilized society.'

The incident came amid escalating violence in Chinese-ruled Hong Kong, where a student protester died earlier this month after falling from a parking lot during demonstrations.

A 70-year-old street cleaner, who videos on social media showed had been hit in the head by a brick thrown by 'masked rioters,' died on Thursday, authorities said.

Teresa Cheng was injured in London after she was allegedly attacked by protesters. China's embassy in Britain has condemned the attack

Cheng was swept away and the Chinese Embassy in the UK later said she was 'besieged' and 'pushed to the ground'

The Food and Environmental Hygiene Department expressed profound sadness on Friday at the death of its worker and said it was providing assistance to his family.

Anti-government protesters paralyzed parts of Hong Kong for a fifth day on Friday, forcing schools to close and blocking some highways as students built barricades in university campuses and authorities struggled to tame the violence.

Protesters used barriers and other debris to block the Cross-Harbour Tunnel that links Hong Kong island to Kowloon district, leading to severe traffic congestion. The government once again urged employers to adopt flexible working arrangements amid the chaos.

The protests escalated in June over a now-scrapped extradition bill that would have allowed people to be sent to mainland China for trial. They have since evolved into calls for greater democracy, among other demands.

Cheng, the embattled Lam's chief legal adviser, played a key role in pushing forward the proposed extradition bill that ignited the protests.

The months-long protests have plunged Hong Kong into its biggest political crisis in decades and pose the gravest popular challenge to Chinese President Xi Jinping since he came to power in 2012. Xi said in Brazil on Thursday stopping violence was the most urgent task for Hong Kong.

Flash mobs again protested at lunch time in the heart of the financial hub and also in the eastern district of Tai Koo, where office workers wearing now-banned face masks chanted 'Liberate Hong Kong, revolution of our time.'

'Things that happened in these few months have made people heartbroken,' said a 31-year-old office assistant who gave her name as Nicole.

'The government only came out to condemn rioters ... They have never thought why so many rioters have emerged in our city and why ordinary citizens support them,' she said.

Detained: A man is pinned to the ground by riot police wearing helmets in the centre of Hong Kong yesterday as demonstrators blocked roads and occupied the city centre for a third day running

Clashes: A riot police officer with a baton scuffles with a protester in the Central business district of Hong Kong yesterday

Injured: An anti-government protester with a bandaged face is held down by a riot police officer with a shield yesterday

Violence has surged in Hong Kong this week after a 22-year-old student died falling from a parking garage during clashes

Thousands of students remain hunkered down at several universities, surrounded by piles of food, bricks, petrol bombs, catapults and other homemade weapons.

Police said the prestigious Chinese University had 'become a manufacturing base for petrol bombs' and the students' actions were 'another step closer to terrorism.'

Around 4,000 people, aged between 12 and 83, have been arrested since the unrest escalated in June.

The demonstrations have paralyzed parts of the city and battered the retail and tourism sectors, with widespread disruptions across the financial center and no end in sight to the violence and vandalism.

Video footage of the Chinese People's Liberation Army garrison headquarters near Hong Kong's Central business district on Friday showed more than a dozen troops conducting what appeared to be anti-riot drills against fake protesters carrying black umbrellas.

The anti-government protests have taken a heavy toll and Hong Kong was expected to confirm on Friday it had fallen into recession for the first time in a decade amid concerns the economy could be in even worse shape than feared.