Four former pro-democracy politicians, including Claudia Mo, Kwok Ka-ki, Jeremy Tam and Gary Fan were driven away from three separate prisons across Hong Kong around dawn on Tuesday.
Security was tight with patrols of police officers, and access to some roads to the prisons restricted for hours beforehand.
Since large and sustained pro-democracy protests erupted in Hong Kong for most of 2019, China has cracked down on the democratic opposition as well as liberal civil society and media outlets under sweeping national security laws.
The 47 pro-democracy campaigners were arrested and charged in early 2021 with conspiracy to commit subversion under a Beijing-imposed national law which carried sentences of up to life in prison.
Forty-five of these were convicted following a marathon trial, with sentences of up to 10 years. Only two were acquitted.
All four had been denied bail since being charged and were remanded in custody for nearly two years before the trial started in early 2023. All four had pleaded guilty, and were sentenced to four years and two months imprisonment.
Mo, Kwok and Tam were former members of the Civic Party, once one of Hong Kong's leading pro-democracy parties, which was disbanded in early 2024 amid the national security crackdown.
Mo resigned from the Civic Party in 2016 and founded the localist group HK First with Fan of the Neo Democrats.
The democrats were found guilty of organising an unofficial "primary election" in 2020 to select candidates for a legislative election. Prosecutors accused the activists of plotting to paralyse the government by engaging in potentially disruptive acts had they been elected.
Western governments including the US called the trial politically motivated and had demanded the democrats be freed.
Hong Kong and Beijing, however, say all are equal under the national security laws and the democrats received a fair trial.
