Six weeks after China imposed a national security law on Hong Kong, police moved in on media tycoon Jimmy Lai, one of the most prominent critics of Beijing in the city.

Lai, 71, was whisked away from his home on Monday morning by police, part of a citywide operation that also saw eight other men arrested, including several of his senior executives. In the evening, police arrested pro-democracy activist Agnes Chow Ting on charges of inciting secession under the new law.

Hundreds of police descended on Lai’s corporate Next Digital headquarters, where his flagship Apple Daily is produced. Police ignored staffers’ questions on what legal grounds they had for entering. Apple Daily’s editor-in-chief Ryan Law tried to report events breaking in his own newsroom via Facebook