Hong Kong police fired tear gas at pro-democracy protesters in the early hours of Wednesday as demonstrators marked the one-month anniversary of the mask ban.
Protesters were seen setting up makeshift barricades in Tseung Kwan O, a residential area in the city, where early on Monday, a university student reportedly fell off an upper floor of a carpark building after police fired tear gas.
Hospital officials said on Tuesday the student was fighting for his life.
Police could not immediately provide details.
Hong Kong Chief Executive Carrie Lam said investigations would be carried out to determine exactly what happened, and that the case drove home the government’s message that violence must cease.
Late on Wednesday, China’s Vice Premier Han Zheng said Beijing supports more aggressive measures to tackle the unrest that has roiled the city.
Han said the protests were damaging the “one country, two systems” formula under which the Asian financial hub has been governed since its handover from Britain to Beijing in 1997.
The demonstrations began in the autonomous Chinese city over a since-scrapped extradition bill and escalated in mid-June.
Protesters have kept up their calls for universal suffrage and an independent inquiry into police behaviour, among other demands.
While the number of people who take part in the mostly weekend rallies has dwindled from the millions who participated in June, the violence and vandalism have escalated.
Authorities have refused permits for many recent protests, making them illegal from the outset and activists liable to be arrested.
The past five months of anti-government protests in the former British colony represent the biggest popular challenge to Chinese President Xi Jinping’s government since he took over leadership in late 2012.
Protesters are angry at China’s perceived meddling with Hong Kong’s freedoms, including its legal system, since the Asian financial hub returned to Chinese rule in 1997. China denies the accusation.