Pro-democracy activist Chow Hang Tung has been arrested by Hong Kong police on the 32nd anniversary of the 1989 Tiananmen Square crackdown.
Ms Chow is vice chairwoman of the Hong Kong Alliance which organises annual vigils for victims of Beijing's deadly crackdown on democracy protesters.
She has been arrested for promoting unauthorised assembly.
It comes as Hong Kong has banned the vigil for the second year running, citing coronavirus restrictions.
Hong Kong and Macau are the only places in Chinese territory where people can commemorate the deadly 1989 crackdown on pro-democracy protesters.
But this year, authorities in Macau also banned the vigil for the second year in a row, saying it would violate local criminal laws.