Hong Kong’s national security police arrested five executives of the pro-democracy Apple Daily newspaper for suspected breaches of the national security law, local news outlets reported Thursday, as the government escalated its campaign against well-known activist and media tycoon Jimmy Lai.

Those arrested included apple daily Editor-in-Chief Ryan Law and Next Digital Ltd. Chief Executive Officer Cheung Kim-hung, as more than 100 police officers descended on the newspaper’s Hong Kong headquarters.

Lai, who founded Next Digital, has been the most high profile target of the government’s push against democracy advocates in the former British colony and is currently serving more than year in prison for attending unauthorized protests. On Thursday morning, trading of Next Digital shares was halted, without any reason being given.