Police said on Sunday they have charged 47 people with conspiracy to subvert state powers under the National Security Law. They said 39 were men and eight were women, and they were aged from 23 to 64.
They said they would be detained overnight and would be brought to West Kowloon court for mention after 11am on Monday.
The pro-democracy politicians and activists - who were arrested last month - are among 55 arrested on suspicion of "subverting state power" for their involvement in primary elections last July - that were intended to choose candidates for Legco polls that never took place.
Officials have said the primaries were an attempt by the camp to win enough seats to "paralyse the government".
The League of Social Democrats says its vice chairmen, Leung Kwok-hung and Jimmy Sham, were among those charged.
The LSD said the two were not allowed bail and are to appear in West Kowloon Magistracy on Monday morning.
Before reporting to police, Mr Leung had said he hoped he could be bailed as he hadn't prepared much, as he had expected to report to police over the case in April.
"I hope all of the quote-unquote suspects will be still on bail today since I don't think the arrests are reasonable."
Before he headed into the police station, one activist, Democratic Party district councillor Andrew Chiu said he'd been spending time with his family in the past few days.
Chiu said the city had entered a new era, and called on people to take care and live for Hong Kong.
Former Civic Party lawmaker Kwok Ka-ki said he was reporting to the police with a calm mind, and urged Hong Kong people to stay strong and "never give up".
He also urged Hongkongers to "keep our early promise that we will always [be] fighting for democracy," he said before reporting to Central Police Station.
Eight out of the 55 earlier arrested have not yet been charged, including former Democratic Party lawmakers James To and Roy Kwong, and American lawyer John Clancey.
Speaking after he walked out of the police station, Clancey said his bail had been extended until May 4th, and he wasn't told why he wasn't charged today.
He said Hong Kong's freedoms and rights were shrinking.
"Recently a lawyer friend of mine commented that even those who were not detained within custody of the police are still living in an increasingly constricted detention centre of Hong Kong," Clancey said.
The European Union issued a statement expressing "great concern" at the charges, and called for the immediate release of the 47.
Last updated: 2021-02-28 HKT 18:29