HONG KONG - In condemning Monday's violence that started early in the morning and later spread to multiple locations, universities and the city centre, Hong Kong's top official said it is "wishful thinking" if protesters thought they would achieve their goals through violence.

Chief Executive Carrie Lam told reporters at around 6pm that violence is not a solution to the problems Hong Kong is facing.

"If there is still any wishful thinking that by escalating violence, the Hong Kong government will yield to pressure to satisfy the so-called political demands, I'm making this statement clear and loud here. That will not happen," Mrs Lam said.

In her brief speech, Mrs Lam said the citywide strike and social unrest on Monday "have caused major consequences for almost everyone in Hong Kong", where people are not able to get to school or even go out to the streets.

She noted that the unrest has led to a larger number of casualties - more than 60 people were injured on Monday, with two in critical condition.

On the case of the man set on fire in Ma On Shan during an argument with protester supporters, Mrs Lam said: "This is a blatant breach of peace, and the rule of law and it's a totally inhumane act that nobody should condone."

She added that there have been "malicious" rumours circulating on social media and called the community to remain calm.

Tensions have boiled over in the city, reaching the business district and campuses following the shooting of a protester early on Monday (Nov 11) morning.

Hundreds in office wear stood along main roads in Central, shouting at riot police who turned up in the business district and calling the officers "murderers" in Cantonese.

At campuses including Chinese University of Hong Kong, Hong Kong Polytechnic University (PolyU) , University of Hong Kong (HKU) and the Hong Kong University of Science and Technology (HKUST), riot police fired tear gas amid a showdown with anti-government protesters, who had set up barricades in the schools.

The Hong Kong government, in a statement on Monday afternoon, urged protesters to remain "calm and rational".

"Protesters should stop all acts that threaten others' safety and obstruct police's lawful execution of duty," it said.

In a statement, police said that one officer had fired his gun and a man was shot in Sai Wan Ho district, east of Hong Kong's main island, at about 7.20am. They added that officers had also drawn their weapons in Sha Tin and Tung Chung.

A live broadcast earlier showed a police officer drawing his sidearm as he tries to detain a masked man at a road junction that had been blocked by protesters.

Another masked man then approaches the officer and was apparently shot in the chest area, quickly falling to the ground, clutching his left side. Some reports said he was shot in the abdomen.

Seconds later, two more live rounds were fired by the officer during a scuffle and another masked man fell to the ground, although the footage was less clear as to whether he was hit.

Police could later be seen detaining the two men on the ground. The first man had a pool of blood next to him, his body limp as officers moved him around and apparently tried to tie his hands. The second man was conscious and talking.

The police, in a statement on Facebook, dismissed as "totally false and malicious" online rumours that they had ordered officers to use their firearms "at will". They also reaffirmed their commitment to upholding "strict guidelines and orders regarding the use of force".

Local broadcaster RTHK said a live video posted by "Cupid News" showed at least one protester shot at close range. Police had fired three shots.

At around 10am, riot police fired tear gas as protesters set fire to cardboard and other debris at one of the road blocks in Sai Wan Ho.

The protesters in Sai Wan Ho were among various groups across the city who sought to disrupt traffic as part of a planned strike on Monday, crippling train lines with the closure of 25 MTR stations and affecting major roads.

A commuter, who gave her name only as Madam Wong, said she had waited for the bus outside Victoria Park in Causeway Bay for nearly half an hour to get to her job in Kowloon Tong, where she works as a sales assistant.

"I told my manager and she said not to worry. It's difficult but police really shouldn't shoot young people, that's not right.

"Yes the protesters built the barricades to disrupt traffic first but this is only because the government isn't listening, that's why they have to resort to this. As adults, we try to be understanding, our young people are fighting for our future, what is a bit of inconvenience for us?"

Separately, a video showing a man being set on fire after an argument with a group of people in Ma On Shan went viral on social media.

The man, who was seen with an injury on his head, had reportedly been shouting to the group of young people that they were not Chinese but British, RTHK reported. That prompted the group to tell him to go back to the Greater Bay Area.

Another person later squirts petrol on the man, setting him alight. The victim is then seen flailing as he is engulfed in flames.

RTHK reported that the police confirmed it had received numerous reports of the incident. A source told RTHK the victim was in critical condition.

Besides disruptions to train and bus services, businesses were also affected with Sogo mall shutting both its Causeway Bay and Tsim Sha Tsui outlets on Monday, while Pacific Place also closing early.

In Central, the working crowd lined up along the roads at lunch time, shouting at riot police in the business district.

Hong Kong's stock market was down 2.9 per cent in mid-afternoon trade, outpacing losses in other parts of the region.

The Labour Department on Monday urged employers to have flexible work arrangements for staff, given the situation.

The police said radicals blocked the Cross Harbour Tunnel at Hung Hom towards Hong Kong Island, Tate's Cairn Tunnel at Sha Tin towards Diamond Hill and at Tuen Mun Road near Castle Peak Road towards Kowloon.

HKUST had on Sunday said that the "mass-scale malicious vandalism on Friday" will take time to repair and classes were cancelled on Monday.

"The incident has caused many HKUST staff and students to start worrying about their personal safety. The government must propose feasible solutions to the current social disputes so that peace and order can be restored in the entire society," HKUST said on Sunday.

At least eight universities and institutes, including HKU, Education University, PolyU, and Baptist University cancelled classes on Monday, while four universities including CUHK and PolyU say classes will remain suspended on Tuesday.

The call for a strike and class boycott comes after a day of angry clashes in the New Territories and Kowloon. The confrontations lasted into the small hours of Monday morning in Mong Kok, where police deployed a water cannon.

Police said that as at 11.30pm on Sunday, 88 people were arrested for offences including unlawful assembly, possession of offensive weapon, criminal damage, and using facial covering while at an unlawful assembly.