Police in Hong Kong have charged 47 activists with "subversion", in the largest use yet of the territory's controversial security law.
The 47, among a group of 55 arrested in dawn raids last month, were told to report to police stations for detention ahead of court appearances on Monday.
Beijing enforced the law criminalising "subversive" acts last year, saying it was needed to bring stability.
Critics say it has silenced dissent and stripped Hong Kong of its autonomy.
The law came into force after a series of mass pro-democracy protests in 2019, some of which turned violent.
On Monday, hundreds of protesters gathered to show support at the West Kowloon Magistrates Court in Hong Kong where the 47 pro-democracy activists were due to face charges of conspiracy to commit subversion.
As supporters queued for seats at the hearing, many dressed in black - the colour protesters have been wearing while demonstrating - some chanted slogans including "liberate Hong Kong, revolution of our times" and "fight for freedom, stand with Hong Kong".
Police warned those gathered to split into groups of no more than four or face fines.
Who has been charged?
Those ordered to report to the police - 39 men and eight women, aged between 23 and 64 - are pro-democracy activists who had helped run an unofficial "primary" election last June to pick opposition candidates for 2020 legislative elections, which were then postponed.
Chinese and Hong Kong officials say the primary was an attempt to overthrow the government.
On Sunday, Hong Kong police said in a statement: "Police this afternoon laid a charge against 47 persons... with one count of 'conspiracy to commit subversion'."
They are some of the territory's best-known democracy campaigners.
They include veterans such as Benny Tai and Leung Kwok-hung, and younger protesters like Gwyneth Ho, Sam Cheung and Lester Shum.
Jimmy Sham, 33, a key organiser of the 2019 protests, remained defiant as he went to the police station.
"Democracy is never a gift from heaven. It must be earned by many with strong will," he said. "We will remain strong and fight for what we want."
Before turning herself in, Gwyneth Ho posted: "I hope everyone can find their road to peace of mind and then press forward with indomitable will."
Sam Cheung said: "I hope everyone won't give up on Hong Kong... fight on."
The charges carry a maximum term of life imprisonment. Bail is unlikely. Benny Tai said his chances were "not too great".
About 100 people have so far been arrested under the security law, including prominent China critic and media tycoon Jimmy Lai, who was denied bail and is in detention awaiting trial..
No trials have yet begun in full. The first is expected to be that of Tong Ying-kit, who is accused of riding a motorcycle into police officers last July. He appeared in court in November to enter a not guilty plea. He is expected to be tried by three judges rather than a jury.
Amnesty International described the January raids that detained the 55 as "the starkest demonstration yet of how the national security law has been weaponised to punish anyone who dares to challenge the establishment".
What is in the National Security Law?
A former British colony, Hong Kong was handed back to China in 1997 but under the "one country, two systems" principle.
It was supposed to guarantee certain freedoms for the territory - including freedom of assembly and speech, an independent judiciary and some democratic rights - which mainland China does not have.
But the National Security Law has reduced Hong Kong's autonomy and made it easier to punish demonstrators.
The legislation introduced new crimes, including penalties of up to life in prison. Anyone found to have conspired with foreigners to provoke "hatred" of the Chinese government or the Hong Kong authorities may have committed a crime.
Trials can be held in secret and without a jury, and cases can be taken over by the mainland authorities. Mainland security personnel can legally operate in Hong Kong with impunity.
After the law was introduced, a number of pro-democracy groups disbanded out of fears for their safety.
Responding on Sunday, UK Foreign Secretary Dominic Raab said the latest charges demonstrated how the law was being used to "eliminate political dissent".
The decision to charge 47 Hong Kong politicians & activists for subversion under the NSL is deeply disturbing. It shows in the starkest terms the NSL being used to eliminate political dissent rather than restore order - contrary to what the Chinese Government promised— Dominic Raab (@DominicRaab) February 28, 2021
"The National Security Law violates the Joint Declaration, and its use in this way contradicts the promises made by the Chinese government, and can only further undermine confidence that it will keep its word on such sensitive issues," he added in a statement.