Demosisto members Nathan Law and Agnes Chow also said they were stepping down from the group.
After China largely brought the virus under control, hundreds have been infected in Beijing and cases have emerged in neighbouring Hebei province.
The Civil Human Rights Front said the force had rejected its applications for rallies on July 1, the 23rd anniversary of the former British colony's handover to China.
China says the national security should worry only those who don't abide by the legislation but Hong Kong democracy activist Joshua Wong says he will be targeted.
The Covid-19 outbreak has been linked to the largest wholesale food market in Beijing, leading to a partial lockdown of the city after the first case was announced on June 11.
Michael Kovrig and Michael Spavor were detained in what was widely seen as a retaliatory measure against Canada after Huawei executive Meng Wanzhou's December 2018 arrest in Vancouver.
European Commission President Ursula von der Leyen and European Council President Charles Michel had video calls with Chinese Premier Li Keqiang and President Xi Jinping, where they discussed ties, as well as China's security law for Hong Kong.
China released some details of the legislation late Saturday, heightening fears that the central government is tightening its grip on Hong Kong after months of anti-government protests last year.
The agency for semi-autonomous city will collect intelligence and handle crimes against national security, official Xinhua news agency reports.
Stand-off between Indian and Chinese border troops is the culmination of festering tensions between the two sides over territory that has been contested for more than a century.
Making sense of what led to the crisis and how it will impact Sino-Indian relations.
The resurgence of Covid-19 in China's capital over the past week has been linked to the city's massive Xinfadi food centre, also raising fears over the hygiene of the imported fish.
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