Activists have vowed to fight on after a man was shot with a live round by police during violent clashes in Hong Kong, which saw tens of thousands of protesters take to the streets on China’s National Day.

The anti-government demonstrators, the majority of whom remain peaceful, set out to disrupt the 70th anniversary of communist rule in China, handing out fliers that called the event a “day of mourning” and singing the protest song “Glory to Hong Kong”.

But events took a violent turn after an officer fired a live round directly at a protester, the first such incident during four months of escalating violence on both sides.

The 18-year-old was shot in the torso at close range in the Tsuen Wan district. “Send me to hospital, my chest is hurting. I need to go to hospital,” the injured teenager said in videos shared by local media.

Police commissioner Stephen Lo, said: “The officer was under attack, his life was threatened. He made a very quick decision and shot the assailant. I believe it was his best judgement at the time.”

Mr Lo said the protester was conscious when he was taken to hospital. Local media outlet Apple Daily reported that he remained in a critical condition.

In total, 66 people were injured and more than 180 arrested, according to the South China Morning Post.

Hong Kong protesters out in force after months of turmoil: In pictures Show all 32 1 /32 Hong Kong protesters out in force after months of turmoil: In pictures Hong Kong protesters out in force after months of turmoil: In pictures A protester throws a stone into a building at Hong Kong Polytechnic University on 11 November Reuters Hong Kong protesters out in force after months of turmoil: In pictures Police patrol the streets of Hong Kong the day after an officer shot a protester during a protest on 11 November EPA Hong Kong protesters out in force after months of turmoil: In pictures Riot police stand guard during a protest against police brutality in Hong Kong on 27 October EPA Hong Kong protesters out in force after months of turmoil: In pictures Protesters carry traffic cones to build a barricade during anti-government protests in Causeway Bay, Hong Kong on 11 November Reuters Hong Kong protesters out in force after months of turmoil: In pictures Protesters use obstacles and bricks to block a road in Hong Kong on 11 November AP Hong Kong protesters out in force after months of turmoil: In pictures Graffiti on a window smashed by student protesters in Hong Kong Polytechnic University AP Hong Kong protesters out in force after months of turmoil: In pictures Protesters carry US and British flags during a demonstration in Hong Kong on 11 November Reuters Hong Kong protesters out in force after months of turmoil: In pictures A protester throws a bottle of water as he is shrouded in tear gas during a demonstration in the Tsim Sha Tsui district of Hong Kong on 27 October Reuters Hong Kong protesters out in force after months of turmoil: In pictures Journalists take pictures of police officers as they move to disperse protesters in Hong Kong on 27 October Reuters Hong Kong protesters out in force after months of turmoil: In pictures An man lies injured after being attacked by protesters who suspected him of being an undercover police officer on 27 October EPA Hong Kong protesters out in force after months of turmoil: In pictures A man runs among tear gas during a protest in Hong Kong on 27 October Reuters Hong Kong protesters out in force after months of turmoil: In pictures Protesters gather on a field in the Tsim Sha Tsui district of Hong Kong on 27 October Reuters Hong Kong protesters out in force after months of turmoil: In pictures Pro-democracy protesters turn away from a fire lit outside the Causeway Bay Mass Rapid Transit (MTR) station in Hong Kong on 4 October Getty Hong Kong protesters out in force after months of turmoil: In pictures People rest near rows of riot police officers during a protest in Mong Kok, Hong Kong on 27 October Reuters Hong Kong protesters out in force after months of turmoil: In pictures Pro-democracy protesters hold umbrellas as police fire tear gas at them ouside Tai Koo MTR station in Hong Kong on 3 October Getty Hong Kong protesters out in force after months of turmoil: In pictures Hong Kong police fire a water cannon from the central government office at protesters during a mass rally on the 70th anniversary of the founding of communist China on October 1 AFP/Getty Hong Kong protesters out in force after months of turmoil: In pictures Protesters burn a Chinese national flag during a mass rally on the 70th anniversary of the founding of communist China on 1 October AFP/Getty Hong Kong protesters out in force after months of turmoil: In pictures Protesters remove signs celebrating the 70th anniversary of the founding of communist China during a mass rally in Hong Kong on 1 October AFP/Getty Hong Kong protesters out in force after months of turmoil: In pictures Cardboard boxes set alight by protesters burn in the streets of Hong Kong during a mass rally on the 70th anniversary of the founding of communist China on 1 October EPA Hong Kong protesters out in force after months of turmoil: In pictures An anti-China banner has been placed in a barricade during a mass rally on the 70th anniversary of the founding of communist China on 1 October EPA Hong Kong protesters out in force after months of turmoil: In pictures A pro-democracy protester runs away after police fire a tear gas canister in Hong Kong's Wong Tai Sin district on October 4 Reuters Hong Kong protesters out in force after months of turmoil: In pictures Protesters run after police fire tear gas during a mass rally on the 70th anniversary of the founding of communist China on 4 October AFP/Getty Hong Kong protesters out in force after months of turmoil: In pictures Pro-democracy protester take cover after police fire a tear gas canister in Hong Kong's Wong Tai Sin district on 4 October Reuters Hong Kong protesters out in force after months of turmoil: In pictures The rally comes after months of protests on the streets of Hong Kong which began in oppposition to a proposed extradition bill EPA Hong Kong protesters out in force after months of turmoil: In pictures The extradition bill would have allowed the government to extradite people to China if they were facing certain criminal charges AFP/Getty Hong Kong protesters out in force after months of turmoil: In pictures Opposition to the bill stems from the fear that the Chinese government would abuse this power for political or commercial reasons EPA Hong Kong protesters out in force after months of turmoil: In pictures Protesters soon came to demand greater freedom and universal suffrage under the One Country, Two Systems principle AFP/Getty Hong Kong protesters out in force after months of turmoil: In pictures Protesters are wearing black to symbolise opposition to China as they take to the streets in a "day of grief" while the Chinese state celebrates the 70th anniversary of its communist founding AFP/Getty Hong Kong protesters out in force after months of turmoil: In pictures A protester charges forward holding umbrellas as a mass rally breaks out in violence in Hong Kong on 1 October AFP/Getty Hong Kong protesters out in force after months of turmoil: In pictures A protester pours water on a tear gas canister fired by police during a mass rally on the 70th anniversary of the founding of communist China on 1 October Reuters Hong Kong protesters out in force after months of turmoil: In pictures A protester carries a vandalised Chinese flag through Hong Kong during a mass rally on the 70th anniversary of the founding of communist China on 1 October EPA Hong Kong protesters out in force after months of turmoil: In pictures Protesters carry a banner that denounces the celebration of the 70th anniversary of the founding of communist China on 1 October EPA

Dominic Raab, the UK foreign secretary, condemned the use of live rounds, saying that “whilst there is no excuse for violence, the use of live ammunition is disproportionate, and only risks inflaming the situation”.

Earlier in the day, tens of thousands attended a march on Hong Kong Island, defying a police ban and risking arrest for participating in an unauthorised assembly. Demonstrators dressed in black chanted the now-enshrined protest anthems of “fight for freedom! Stand with Hong Kong!” and “Hong Kong add oil!” – a Hong Kong saying akin to “Keep going!”, as they marched in the sweltering heat of the day.

US and British flags waved above the crowds, without what appeared to be a single Chinese flag in sight.

A 29-year-old protester named Tse, who attended the march until he was tear gassed during dispersal operations in the upscale shopping district of Causeway Bay, said that by protesting on National Day, demonstrators intended to “embarrass the Chinese Communist Party” while garnering international attention.

“They are really scared of losing face on the National Day, so we want to let them know that we are going to fight for what we want and we are not scared of any violent means of suppressing us and our ideas. This is another way for us to express and magnify what we are fighting for.”

Twenty five public transport stations were closed throughout the day and dozens of shopping malls announced they would be closed after the police issued a statement on Monday warning of violent acts planned for National Day.

Smaller rallies were held in six districts, in front of government offices, temples and playgrounds. Clashes began early in the day in Tuen Mun district, when protesters threw bricks and other random objects at officers who responded with tear gas and water cannons.

The police posted images of an officer injured by corrosive liquid that they say “rioters” threw during the clash in Tuen Mun.

Local broadcaster TVB said that one of its reporters sustained similar injuries.

In other districts, protesters blocked major roads and formed defensive lines with umbrellas and metal street railings that they connected with zip ties. Some protesters armed themselves with hiking sticks and stalks of bamboo.

In San Po Kong district, where protesters set small fires in the street, a university student named Truman, who was not taking part in the protests, said that an officer pointed his shotgun directly at him and others after they jeered at police from an elevated footbridge.

“We had nothing but our words,” he said. “For the police to respond that way to unarmed people, it makes me feel that they think they are above the law, that they have no guidelines anymore.”

An anti-government protester is arrested by police officers protesting during China National Day (EPA)

As clashes continued to escalate into the night, multiple media companies, including local broadcaster RTHK and the South China Morning Post, pulled reporters from the streets as tear gas and rubber bullets were employed.

Many arrests were carried out violently as protesters set fires and threw petrol bombs in neighbourhoods on the peninsular side of the territory after Hong Kong Island protest sights were largely cleared by riot police.

The citywide protests initially broke out in June over a controversial bill that would have allowed extraditions to China.

The bill has since been withdrawn, but protesters’ demands have grown to include an independent inquiry into police violence and electoral reforms.

After more than a century as a British colony, Hong Kong was returned to China in 1997. The semi-autonomous territory was assured a high degree of autonomy until 2047 but many residents fear that basic rights and freedoms enshrined in the city’s constitution are under threat.

The clashes in Hong Kong contrasted with anniversary celebrations in Beijing, which included a parade showcasing the country’s military might.

Among those attending was Hong Kong chief executive Carrie Lam, who demonstrators have repeatedly called on to resign due to her failure to handle the crisis.