"This has sent shudders through the industry," Elaine Yu, a Hong Kong-based reporter for the Wall Street Journal, told CNN's Chief Media Correspondent Brian Stelter on "Reliable Sources" Sunday.

"It raises important new questions about how media outlets can report on topics that are now considered highly sensitive."

During the raid, Apple Daily's CEO Cheung Kim Hung, COO Chow Tat Kuen and chief editor Ryan Law, along with the deputy chief editor and online editor were arrested by police.

The arrested people were accused of colluding with foreign forces to endanger national security.

Some 500 policemen raided the offices of pro-democracy paper Apple Daily in Hong Kong by alleging that the report published by it breached a national security law.

Police also arrested the editor-in-chief and four other executives at their homes. It also froze HK$18m ($2.3m; £1.64m) of assets owned by three companies linked to Apple Daily, reports BBC.

Jimmy Lai is the owner of the paper. He is currently in jail and facing several charges.

Apple Daily is known to be critical of the mainland Chinese leadership, reports BBC.