Hong Kong police have shot a protester with live ammunition for the first time in four months of demonstrations, marking a major escalation in the use of force on a day when China celebrated 70 years of Communist party rule with a triumphalist military parade.

Protests called to mark a “national day of grief” drew tens of thousands of people on to the city’s streets, across six areas, in the most widespread show yet of public anger towards Beijing.

Some gathered in central Hong Kong, while others met up across the harbour in Kowloon and the New Territories beyond. Initially peaceful, the demonstrations turned into running battles that in some places ran on past midnight. Authorities shut down nearly half the city’s metro stations in an attempt to contain the violence.

Police in full riot gear used water cannon and barrages of teargas, while protesters threw molotov cocktails, built barricades, attacked metro stations and lit fires in the street.

Anti-government protesters vandalise an MTR public transport station in Hong Kong.
Anti-government protesters vandalise an MTR public transport station in Hong Kong. Photograph: Kin Cheung/AP

The scenes, though extremely violent, did not mark a departure from previous protests until mid-afternoon, when a policeman fired a bullet into an 18-year-old high school student’s chest in Tsuen Wan district.

Images shared by local media showed the protester lying on the ground begging for help as he bled from his injury. “Send me to hospital, my chest is hurting. I need to go to hospital,” he said.

Although warning shots have been fired during other protests, police have caused serious injury with rubber bullets and beanbag rounds, and groups including Amnesty International have condemned excessive use of force, this was the first time someone has been hit with a live round.

A video posted by the Hong Kong University Students Union appeared to show the policeman shooting the student at point blank range with a pistol, as a group of protesters attacked another officer.

Commissioner of police Stephen Lo Wai-chung said the use of a live round was “lawful and reasonable”, and the man had been arrested for assaulting a police officer after he was taken to hospital.

The officer opened fire after protesters attacked a policeman who was lying on the ground, Lo told the SCMP. “So when an officer felt that officers’ lives were under serious threat, he fired a live round.” Six live rounds were fired in total during the protests on Tuesday, he added.

The UK said the use of live ammunition was “disproportionate”, while Amnesty International called for an urgent and independent investigation.

Crowds gathered in central Hong Kong, where police were using water cannon and teargas, fell silent when they heard someone had been shot.

But violence soon resumed, and in some places intensified, as protesters faced off with police into the evening. Later a journalist from the local RTHK network was taken to hospital after a projectile hit him in the face, prompting the network to withdraw all its reporters from the streets.

Health authorities said at least 66 people were injured in protests, the youngest only 11 and the oldest 75. Two were in a critical condition, and two in a serious condition.

Hong Kong has been gripped by protests since June. Sparked by a controversial extradition bill, they have morphed into a wider and increasingly violent anti-government movement channelling residents’ anger and frustration at the erosion of rights under Chinese rule.

Tuesday’s marchers had already defied a police ban to turn out in large numbers. Organisers wanted to mark the 70th anniversary of communist China as a day of mourning not celebration, and tens of thousands came out in response.

“We want to show people this is not a happy anniversary,” said Richard Hung, who works in the technology sector. “The CCP [Chinese Communist party] has killed or injured so many millions of people already. We have come out today, because if we don’t, we may not have another chance.”

For the first few hours, the main march through the city centre was peaceful, with protesters dressed largely in black singing “glory to Hong Kong”, scattering paper money used for funeral offerings, and scrawling protest slogans on streets, bus stations and shops seen as pro-Beijing.

Graffiti included anti-China messages mocking the day’s celebrations across the border, calls for freedom and democracy, and a warning with a prophetic ring that has become a protest staple: “if you burn, we burn with you”.

Many families and young children were among the crowds at first. “You can see, we don’t have any protective gear,” said Terrence, a logistics worker walking with his eight-year-old daughter. “We want freedom, and don’t want to belong to China.”

Riot police clash with protesters in the Sha Tin district of Hong Kong.
Riot police clash with protesters in the Sha Tin district of Hong Kong. Photograph: Jorge Silva/Reuters

Still, a large proportion of protesters wore face masks or carried umbrellas, to stop them being filmed or identified by authorities who have already arrested hundreds. Some have been charged with rioting, which carries a sentence of up to 10 years.

Police had said ahead of Tuesday that they feared violent protests, and made a string of raids and arrests, claiming to have uncovered bomb-making equipment and ingredients.

Aggressive policing and the scale of the recent violence fuelled fears that authorities might use it as a pretext to bring in draconian emergency legislation, which would allow the government to arrest people at will, and control the press and communications, in the name of stability.

“It seems there is no sign of this coming to an end until the government is determined to clamp down,” said pro-Beijing lawmaker Junius Ho Kwan-yiu, who has previously called for an emergency law, in a statement carried by the South China Morning Post.

The day began with an episode of police aggression, when officers used pepper spray on a small group of protesters outside the government’s official flag-raising ceremony and national day reception, which was closed to the public.

It was calm throughout the morning, as Beijing celebrated its anniversary and rise to super-power status with a military parade showing off its latest hardware, and a civilian procession celebrating everything from communist heroes to agriculture and bicycles.

Hong Kong’s protesters began turning out only after those events wrapped up, preparing their own response to mark the day.

“It’s National Day but there is nothing to be happy about in Hong Kong,” said Sarah, 17. “We’re under one party rule and the Communist party controls our government.”