More than 50 of Hong Kong's most prominent pro-democracy activists and politicians have been arrested in the biggest crackdown since China imposed a draconian security law last year. About 1,000 police took part in morning raids on 72 premises across the city. Those held helped run an unofficial "primary" to pick opposition candidates ahead of postponed 2020 elections. They are accused of trying to "overthrow" the government. Activists say the new law aims to quash dissent. China's government imposed the legislation on the semi-autonomous territory in June, saying it was necessary to curb months of sometimes violent pro-democracy protests. Beijing defended Wednesday's arrests, with Foreign Ministry spokeswoman Hua Chunying saying they were needed to stop "external forces and individuals [colluding] to undermine China's stability and security". But the crackdown appeared to confirm the fears of many who warned about the reach of the law, with Amnesty International saying the arrests are "the starkest demonstration yet of how the national security law has been weaponised to punish anyone who dares to challenge the establishment".