Hong Kong's national security police detained two former senior staff of shuttered pro-democracy newspaper Apple Daily on Wednesday, shortly after they arrested the paper's former executive editor-in-chief.

Local media reported that the paper's former deputy chief editor Chan Pui-man and managing editor Fung Wai-kong, who had already been arrested for "colluding with foreign forces", were detained again while on police bail.

A police source told AFP that former executive editor-in-chief Lam Man-chung was detained on Wednesday morning.

In two statements, police confirmed the arrest of a 51-year-old former newspaper editor for "collusion with foreign forces", a national security crime, and the withdrawal of bail for a 51-year-old woman and a 57-year-old man over the same allegation.

Lam is the eighth employee of Apple Daily arrested within a month under a sweeping national security law that Beijing imposed on Hong Kong last year after huge and often violent democracy protests.

Lam's girlfriend told local media Citizen News that the arrest was made at home at dawn. Police seized his computers and mobile phones for investigation.

"Nowadays working in journalism, one wouldn't be unprepared psychologically (for this)," she told Citizen News.

Chan was among the five executives who were arrested in mid-June after hundreds of police raided the paper's newsroom.

Apple Daily, an unapologetic backer of the democracy movement, put out its last edition late last month after its top leadership was arrested and its assets frozen under the security law.

Lam Man-Chung, then executive editor in chief  of Hong Kong's pro-democracy 'Apple Daily' newspaper on the day before it printed its final edition
Lam Man-Chung, then executive editor in chief of Hong Kong's pro-democracy 'Apple Daily' newspaper on the day before it printed its final edition AFP / Anthony WALLACE

Lam was the editor who oversaw that final edition, ending the paper's 26-year run.

Fung, also a former chief opinion writer for the Apple Daily's English website was arrested at the city's airport as he tried to leave the city just a few days after the paper was shut.

Authorities said Apple Daily's reporting and editorials backed calls for international sanctions against China, a political stance that has been criminalised by the new security law.

The tabloid's owner Jimmy Lai, 73, is currently in prison and has been charged with collusion alongside two other executives who have been denied bail.

They face up to life in prison if convicted.

Among the others arrested, but currently on bail, are the paper's chief operating officer, executive chief editor and a leading editorial writer.

The paper's sudden demise was a stark warning to all media outlets on the reach of a new national security law in a city that once billed itself as a beacon of press freedom in the region.

The Hong Kong Journalists Association expressed indignation and shock over the arrests.

The group last week published its annual report saying the city's media freedoms were "in tatters" as China remoulds the once outspoken business hub in its own authoritarian image.