Hong Kong police have made their first arrests under a new "anti-protest" law imposed by Beijing, as crowds marked 23 years since the end of British rule.
Nine people were held accused of violating the law, including a man with a pro-independence flag. More than 300 others were detained at a banned rally, the BBC reported.
The national security law targets secession, subversion and terrorism with punishments up to life in prison.
Activists say it erodes freedoms but China has dismissed the criticism.
Hong Kong's sovereignty was handed back to China by Britain in 1997 and certain rights were supposed to be guaranteed for at least 50 years under the "one country, two systems" agreement.
The UK has now said up to three million Hong Kong residents will be offered the chance to settle in the UK and ultimately apply for citizenship.
On Wednesday, thousands gathered for the annual pro-democracy rally to mark the handover anniversary, defying a ban by authorities who cited restrictions on gatherings of more than 50 people because of Covid-19.
Police used water cannon, tear gas and pepper spray on demonstrators. One officer was stabbed in the arm by "rioters holding sharp objects", police said. The suspects fled and bystanders offered no help, they added.
One of the nine arrested under the new law, adopted in the wake of last year's widespread unrest, was holding a "Hong Kong Independence" flag. However, some Twitter users said the picture appeared to show a small "no to" written in front of the slogan. The man has not been identified, and it was not clear whether he would be prosecuted.
The legislation has been condemned by numerous countries and human rights activists.
UK Foreign Secretary Dominic Raab called the measures a "flagrant assault" on freedoms of speech and protest.
The UK has also updated its travel advice on Hong Kong, saying there is an "increased risk of detention, and deportation for a non-permanent resident".
US Secretary of State Mike Pompeo said China had broken its promise to Hong Kong's people.
But in Beijing, foreign ministry spokesman Zhao Lijian urged countries to look at the situation objectively and said China would not allow foreign interference in its domestic affairs.
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