The semi-autonomous territory earlier said it has more than 20,000 quarantine wristbands ready for overseas arrivals. But only some of 6,000 wristbands have been activated despite a surge in people returning home this week.
Chan Kin-man was found guilty last year of conspiracy to commit public nuisance for his role in planning and mobilising supporters during the 79-day protest that brought parts of the Chinese-ruled city to a standstill.
Hong Kong's Apple Daily newspaper said Jimmy Lai, the founder of Next Media, was picked up from his home by officers at around 7 am and taken to a police station in the Kowloon neighbourhood.
A trending video in Turkey inaccurately mocks Syrians for being lazy and living off handouts from the government.
Another 86 people died from the virus, according to the national health commission, with all but five in hard-hit Hubei province, where the disease emerged in December.
The move came as city leader Carrie Lam faced criticism in some quarters over her administration's response to the crisis, including calls to halt, or limit, arrivals from the Chinese mainland where the epidemic began.
Out in numbers before the demonstration began, police intervened promptly when the rally turned into an impromptu march. Several units of police in riot gear were seen chasing protesters and several arrests were made.
Executive Director Kenneth Roth of Human Rights Watch says he has been able to enter Hong Kong freely in the past.
Scuffles erupted between police and protesters in Hong Kong on Sunday, with dozens of arrests made, after thousands marched near the border.
Police detained around 400 people for offences including unlawful assembly and possession of offensive weapons, in the protest which organisers said more than a million people attended.
Smaller crowds of protesters in the Mong Kok district set fire to barricades and riot police unleashed 2020's first volleys of tear gas in response.
Police will deploy more than 6,000 officers to deal with potential unrest over the New Year's period, according to the South China Morning Post newspaper, citing unnamed sources.
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