HONG KONG (AP) — Hong Kong authorities arrested media tycoon Jimmy Lai on Monday, broadening their enforcement of a new national security law and stoking fears of a crackdown on the semi-autonomous region’s free press. Police were seen carting away boxes of what they said was evidence at Lai’s pro-democracy Next Digital headquarters.

In the evening, police arrested pro-democracy activist Agnes Chow Ting on charges of inciting secession under the same law, according to tweets by fellow activist Nathan Law, who left Hong Kong for Britain soon after the law took effect. An earlier post on Chow’s official Facebook page said police had arrived at her home and her lawyers were rushing to the scene, and a separate post later confirmed that she had been taken away by police.

Two days after Chinese and Hong Kong officials shrugged off sanctions imposed on them by the U.S., the moves showed China’s determination to enforce the new law and curb dissent in the semi-autonomous city after months of massive pro-democracy demonstrations last year.

The arrest of Lai, two of his sons and several company officers and the search of Next Digital marked the first time the law was used against news media. Next Digital operates Apple Daily, a feisty pro-democracy tabloid, often condemns China’s Communist Party-led government.