Amnesty International on Tuesday urged the Hong Kong government to investigate police use of force during nearly four months of protests, and to encourage Beijing to safeguard protesters' right to peaceful assembly.
Many peaceful protests have degenerated into running battles between black-clad protesters and police, who have responded with tear gas, water cannon, rubber bullets, bean bag rounds and several live rounds fired into the air.
Police, who have also been seen beating protesters on the ground with batons, say they have shown restraint on the streets in the face of increased violence, including protesters hurling petrol bombs at security forces.
"Ordering an independent and effective investigation into police actions would be a vital first step," Joshua Rosenzweig, head of Amnesty's East Asia regional office, said in a report.
"Authorities need to show they are willing to protect human rights in Hong Kong, even if this means pushing back against Beijing's 'red line'."
In 2017, Chinese President Xi Jinping warned in a speech marking the 20th anniversary of Hong Kong's handover to Beijing that any attempt to undermine China's sovereignty was a "red line" that would not be tolerated.
What started as protests over a now-shelved extradition bill that would have allowed criminal suspects to be sent to mainland China for trial have evolved into broader calls for greater democracy and an independent inquiry into police actions.
Activists are also frustrated by what they see as Beijing's tightening grip over the former British colony that was returned to China under a "one country, two systems" arrangement in 1997.
China has said it is committed to the arrangement that ensures freedoms not enjoyed on the mainland, including right of assembly and an independent judiciary, and denies interfering.
In a direct challenge to Communist Party rulers in mainland China, some protesters have targeted Beijing's representative office in Hong Kong, thrown bricks outside the Chinese People's Liberation Army base and set fire to the Chinese flag.
The Asian financial centre is on edge ahead of the 70th anniversary of the founding of the People's Republic on Oct. 1, with authorities eager to avoid scenes that could embarrass the central government in Beijing.
Hong Kong also marks the fifth anniversary this weekend of the start of the "Umbrella" protests, a series of pro-democracy demonstrations in 2014 that failed to wrestle concessions from Beijing.