Wen Wei Po, a newspaper that answers to Beijing’s Liaison Office in Hong Kong, said Koo Sze-yiu was arrested on Friday morning by national security police.
A senior police source confirmed to AFP that Koo had been detained for “incitement to subversion” and that four others had been taken in to assist with their investigation.
The arrest comes days after Hong Kong journalists received a media invitation bearing Koo’s name saying he was planning to protest on Friday outside Beijing’s Liaison Office in Hong Kong ahead of the start of the Olympics.
“Many political activists and Hong Kong citizens have been jailed and cannot spend Lunar New Year with their families because of abuses of Hong Kong’s national security law,” read the invitation, dated 31 January.
“The central government is only concerned with hosting the Winter Olympics to whitewash the situation, and does not care about miscarriages of justice in Hong Kong,” it said.
Koo could not be reached for comment to confirm if he had organised a protest, which was slated to be held at 10 am Friday morning.
The septuagenarian activist, who is terminally ill with cancer, has been jailed multiple times—most notably in 2013 for burning China’s flag to protest against Beijing’s treatment of dissidents on the Chinese mainland.
Protest has been all but outlawed in Hong Kong since the 2019 unrest.
The national security law, enacted in 2020, criminalises “secession, subversion, terrorism and foreign collusion”, and carries a maximum sentence of life in prison.
Hong Kong police have arrested more than 160 people under the law, with about 100 formally charged. Most are denied bail until trial.
The city has also kept strict anti-coronavirus measures that ban gatherings of more than four people for the past two years.
The Olympics opening ceremony kicks off at 8 pm (1200 GMT).
Beijing’s hosting of the global sporting event has largely been overshadowed by a Western diplomatic boycott over China’s human rights record.