Media tycoon Jimmy Lai has been arrested under Hong Kong’s national security legislation, and his newspaper raided, as he was accused of “colluding with foreign powers” in the most prominent arrest since China imposed the controversial law just over a month ago.

Lai’s Apple Daily reported that ten police officers arrived at the 72-year-old’s home at about 7 am (23:00 GMT on Sunday), and later began to live streaming a raid on its headquarters by scores of police who could be seen looking through piles of papers including on reporters’ desks.

The police confirmed the arrest of seven people aged between 39 and 72.

Lai’s is the most high profile arrest since China imposed the security legislation, triggering condemnation from activists within Hong Kong as well as from Western countries who feared the law would be used to crack down on critics and stifle reporting.

On Friday, the United States imposed sanctions on top officials from China and Hong Kong, including chief executive Carrie Lam, accusing them of curtailing the territory’s freedoms.