HONG KONG - An illegal protest rally through Hong Kong's Tsim Sha Tsui spiralled into chaos on Sunday (Oct 20) as protesters began to engage in acts of vandalism and arson even as the police warned of a response.

Signs of trouble started to emerge towards the end of the march near the West Kowloon rail terminus, in a now-familiar pattern. Protesters were seen spraying over the MTR logo with black paint, building barricades and digging up bricks from the ground.

At Tsim Sha Tsui police station, demonstrators tossed multiple rounds of Molotov cocktails at the building and police responded with multiple volleys of tear gas from the upper floors while warning protesters over a loudspeaker to stop. Two hoses were constantly spraying water to douse the flames.

A similar scene played out at the Mong Kok police station, prompting officers inside to raise an orange flag signalling to protesters to disperse or be fired upon.

In more violence, petrol bombs were thrown into the exit of Yau Ma Tei MTR station as well as Mong Kok MTR station, while branches of shops Best Mart 360 and Yoshinoya were attacked by protesters. One demonstrator was seen using an electric chainsaw to cut down a CCTV camera before setting it on fire.

Meanwhile, a Bank of China outlet in Canton Road was fire-bombed, while one of its ATMs was vandalised in Yau Ma Tei. Road blocks were set up on Mong Kok Road and Tong Mi Road, with steel fences, road signs and trash bins, which were then set on fire, causing traffic disruptions.

There were unconfirmed reports of shots being heard and protesters in Yau Ma Tei said tear gas had been fired. Local media reports said that a water cannon firing blue dye was used on Nathan Road.

The organisers of the demonstration went ahead with the march through Tsim Sha Tsui despite a ban on the procession by the authorities, with the territory's train operator bracing for chaos.

Police had banned the march in the city's Kowloon district, citing concerns over public safety, and a court said last Saturday that the destination of the march - the main railway interchange with mainland China - could be attacked and vandalised.

The planned route for the march, aimed at opposing a law banning face masks that was introduced on Oct 5, was from Tsim Sha Tsui to the express rail terminus in West Kowloon.

Members of the Civil Human Rights Front, which was behind million-strong and two-million-strong protests in June, had vowed to carry on marching in their personal capacity despite the ban.

The protesters, numbering in the tens of thousands, stretch banners reading "Free Hong Kong" across the ground, while other posters read "Hong Kongers Resist". Graffiti on one wall read, "Better Dead than Red".

Hong Kong leader Carrie Lam on Sunday pledged to find other ways to assuage concerns about police conduct during the protests if an official probe into key incidents during the turmoil failed to do the job.

Mrs Lam said the Independent Police Complaints Council (IPCC) would focus on controversial episodes during the escalating protests, including an attack by alleged gangsters on protesters in Yuen Long and a police charge at Prince Edward station.

However, Mrs Lam did not outline her plans if the police watchdog's investigation, the findings of which are to be made public by the end of this year, does not pacify angry residents.

"We sincerely hope to show the public the truth about these incidents," she said.

"But if the report of the independent IPCC, when it is delivered, still fails to quell the controversies with a lot of doubts in society, at that time I believe the chief executive and the (Hong Kong) government will definitely think of another way to make a sufficient response to the public," she said.

Security was tightened ahead of the anti-government march, with some public facilities shuttering as pro-democracy leaders called on citizens to join the protest in spite of the risk of arrest.

"Carrie Lam is not listening to us at all. This may work in China but not in Hong Kong," Cheung, a 33-year-old woman wearing a face mask and black T-shirt, symbols of the democracy movement, told Reuters.

She declined to give her first name.

"You can't ask a city that already has freedom to walk backward. You can't close the door and keep everyone inside. You can't do this in an international city," she said, adding she was not afraid of being arrested.

The police issued a warning to protesters in a statement.

"At around 1.30pm, some protesters gathering at Tsim Sha Tsui are blocking the carriageways on Nathan Road near Salisbury Road, and are committing the offence of 'Participating in an unauthorised assembly'," the statement said.

"Police appeal to members of the public to leave immediately. Due to the obstruction of traffic, drivers are advised to stay tuned to the latest traffic arrangement," it said.

In a separate statement issued in the late afternoon, the police said it would conduct dispersal and arrest operations soon, dubbing the protesters rioters.

At the city's high speed rail station in Kowloon, several areas were closed and only passengers with tickets were permitted entry. All food and beverage outlets were also closed.

Members of the group are also asking for reform of the police force, which has come under fire for alleged brutality and a lack of accountability.

In anticipation of chaos breaking out after the march, as has been seen previously following peaceful rallies, the city's train operator shut down the Austin and Tsim Sha Tsui stations from midday on Sunday.

Other stations or exits might also be closed without prior notice, it warned.

Train services were scheduled to end at 10pm, as MTR continued to repair the damages to its facilities. The Airport Express - which runs between Hong Kong Station and the airport - was the only exception.

According to the MTR website, Mong Kok, East Tsim Sha Tsui, Yau Ma Tei, Prince Edward, Austin and Tsim Sha Tsui stations were closed and trains would not stop at those stations.

Train stations have been a common target of protesters who believe MTR Corporation is pro-China.

The unrest in Hong Kong is approaching five months as protesters press the government to give in to their five demands, including amnesty for those arrested and an independent probe into alleged police brutality.

A prayer sit-in last Saturday evening drew hundreds of people to the central business district, while last Friday, protesters formed a human chain along the metro network. Many donned masks in defiance of a ban on covering faces at public rallies.

Prominent human rights activist Jimmy Sham was attacked by hammer-wielding men last week in the gritty Mong Kok district in Kowloon. Pro-democracy lawmakers said the attack was designed to intimidate protesters and incite violence.

Mr Sham heads the CHRF.

Last Saturday, Mr Sham issued a public "Letter to Hong Kong".

"I have been attacked twice within 45 days. In fact, my family and friends have been harassed by different forces as well. I can not compare my wounds with those who suffer from police violence and torture. The pains of my injuries are far less than that of seeing our authority falling. Today, one of us was assaulted severely in Tai Po. I really wish such terrible attack no longer happens," wrote Mr Sham.

He said the Civil Human Rights Front upholds the principle of peaceful, rational and non-violent resistance. However, he said the organisations's commitment to organising peaceful, rational and non-violent rallies and assemblies has been repeatedly objected by the police commissioner of Hong Kong.

"The government doesn't tolerate dissenting opinion, and isn't capable to solve the social problems. Rather, it only attempts to silence people who address the problem. It only shows that the government is deceiving itself," wrote Mr Sham.

He said the CHRF appealed against the police objection to the proposed rally on Sunday, but although his colleagues tried their best to explain the importance of holding the rally to the appeal board, it was rejected.

"Therefore, what we can do is to stand with each other, and face the inevitable fear and challenges tomorrow," he wrote.

"I am moved by the human chain action last night. I received a photo from my friend. The photo portraits a protesters' banner saying, 'we are all Jimmy Sham'. I would like to express my gratitude to everyone. I am moved by your bravery and efforts that make me experiencing a sense of belonging: We are all Hong Kongers," Mr Sham wrote.

Mr Sham wrote that he would like to ask two favours of Hong Kongers.

"First of all, let us connect with and protect each other. Do not label anyone by ethnicity in the movement. I believe that, everyone who joins this path to democracy are our brothers and sisters, regardless of nationality, language, colour and race.

"Second, please take care of yourselves. Go home safely. I send my wish to everyone who take risk and gives themselves for Hong Kong, and my colleague as well as senior fellows who take act of civil disobedience tomorrow," wrote Mr Sham.

He concluded his letter with "Peace be with you. I love you all".

Later in the day, the CHRF issued a statement saying that Mr Sham had left Kwong Wah Hospital.

"He has to continue to receive medical treatment and physical therapy. Thus he will not attend any public events in the coming days. Jimmy expresses his gratitude to everyone who concerns his condition," the statement said.