Hong Kong police put three former journalists with the forcibly-closed Apple Daily newspaper behind bars, making one new arrest and revoking bail for two other arrestees.
National security police arrested former Apple Daily executive editor Lam Man-chung "for enquiries" into an ongoing investigation, the police force and a journalists' association said.
Lam, 51, is being held on suspicion of "conspiracy to collude with a foreign power."
"Police do not rule out the possibility of further arrests," the force said.
"The national security department of the [Hong Kong] police has arrested Lam Man-chung, the former executive editor of the Apple Daily, on suspicion of 'conspiring to collude with foreign forces to endanger national security'," the Hong Kong Journalists' Association (HKJA) said in a statement on its website.
"Several senior editors at the Apple Daily have been arrested in recent months," it said.
"The HKJA expresses indignation at the authorities' repeated targeting of journalists from the same organization," the statement said. "We are also shocked and puzzled as to why police would arrest a former employee of a media organization that has now ceased operating."
Police also revoked bail for two other former top editors at the paper, which was forced to close last month after its assets were frozen during a national security police raid on its headquarters in Tseung Kwan O.
Former Apple Daily associate publisher Chan Pui-man and columnist Fung Wai-kong were taken into custody at police stations in Sau Mau Ping and Wan Chai respectively.
They were first arrested on Jun. 17, on suspicion of the same offense, but later released on bail.
Press freedom "in tatters"
The HKJA said last week that press freedom in Hong Kong is "in tatters" the forced closure of the Apple Daily and the arrests of columnists under the national security law.
Press freedom in the city has been increasingly affected by political "red lines" laid down after the ruling Chinese Communist Party (CCP) imposed its national security law on the city from July 1, 2020, the group said in an annual report published last week.
It listed the arrest of Apple Daily founder Jimmy Lai on charges of "colluding with foreign powers," a forthcoming law banning "fake news," government control over content broadcast by RTHK, and the arrest of a journalist for searching a public database for car license plates for a documentary.
"The HKJA calls on the government not to keep arresting journalists in the name of national security, and creating an atmosphere of fear in the industry," the group said on Wednesday.
Meanwhile, a court in Hong Kong on Wednesday sentenced two students to prison for "rioting" during the siege of the Chinese University of Hong Kong (CUHK) on Nov. 12, 2019.
Cheung Chun-ho, 20, and Tang Hei-man, 25, were among dozens of people who threw bricks, petrol bombs and other objects in a bid to hold off troops of riot police, who fired more than 1,000 tear gas rounds onto the university campus in a single day.
Cheung was sentenced to four-and-a-half years' imprisonment, and Tang to three years, nine months.
Translated and edited by Luisetta Mudie.