China has taken another step towards extinguishing any form of dissent in Hong Kong, hailing police in the city for arresting top editors of a pro-democracy newspaper and warning journalists not to write articles that challenge Beijing.

On Thursday morning, roughly 500 police officers descended on the headquarters of the popular Apple Daily newspaper for the second time in 12 months after accusing its leaders of violating a national security law imposed last year. They arrested three top editors and two senior executives of the tabloid owned by Next Digital founder and democracy activist Jimmy Lai, a fierce critic of Beijing who is serving more than year in prison for attending unauthorised protests...