Six former senior staff members of the now-defunct Apple Daily and its parent company Next Digital on Tuesday pleaded guilty to taking part in a conspiracy to commit national security offences.

The defendants are Next Digital's former CEO Cheung Kim-hung, former editor-in-chief of Apple Daily Ryan Law, former associate publisher Chan Pui-man, former executive editor-in-chief Lam Man-chung, former editor-in-chief of the paper's English section Fung Wai-kong and former editorial writer Yeung Ching-kee.

They pleaded guilty to conspiring to collude with a foreign country or foreign elements to endanger national security between July 2020 and June 2021.

The court heard that they had conspired with founder of Next Digital, Jimmy Lai, and other people to request a foreign country or organisation “to impose sanctions or blockade, or engage in other hostile activities” against the Hong Kong and Chinese governments between July 2020 and June 2021.

Mitigation and sentencing was adjourned until after the national security trial of Lai, which is scheduled to begin on December 1 and is expected to last for 30 days.

Some of the six will give evidence in Lai's trial, while the lawyer for Cheung revealed in court that his client will be a prosecution witness.

During Tuesday's hearing, prosecutor Anthony Chau said Apple Daily was used as a platform to advocate for foreign sanctions.

"The impugned content took the form of, among others, articles purported to be news coverage of current issues, commentary articles, and appeals or propaganda directly and unlawfully advocating political agenda," Chau said.

Chau also cited over 160 articles published by Apple Daily, some dating as far back as March 2019, which he said included seditious statements and appeals to the public to take part in pro-democracy protests that year. (Additional reporting by Reuters)