Lai is one of the most prominent figures to be prosecuted under Hong Kong's national security law, which Beijing imposed in 2020 following huge pro-democracy protests in the city.

Western countries and rights groups have demanded the release of the 77-year-old founder of the now-shuttered tabloid Apple Daily, who has been behind bars since December 2020.

Lai first took the witness stand in November and prosecutors began cross-examination on Thursday after defence lawyers wrapped up their questioning.

The offence of collusion with foreign forces carries a maximum penalty of life in prison. Lai also faces a charge related to "seditious publications".

On Thursday, Lai said he set up a paid "consultancy" arrangement in 2017 where retired United States general Jack Keane and former US deputy secretary of defence Paul Wolfowitz would meet with Tsai Ing-wen, Taiwan's leader at the time.

Lai said that, shortly after Trump became president in 2016, Tsai's government had wanted insight into the latest US thinking on the self-ruled island.

"(Keane and Wolfowitz) were both my friends and they seemed to know about the (Trump) administration's sentiments and thinking toward Taiwan," Lai told the court.

Prosecutors presented messages in court they said showed Lai supporting a stronger US military presence in Taiwan.

"I suggest to you that the purpose of engaging (Keane and Wolfowitz) was to give advice to Taiwan for a military upgrade," said prosecutor Anthony Chau.

"I disagree," Lai replied.

Prosecutors have previously displayed a chart in court titled "(Lai's) external political connections" that featured headshots of political and diplomatic figures in the US and Britain.

At the start of his testimony, Lai said his newspaper championed democracy and freedom, adding that he had always disavowed violence.

Apple Daily was forced to close in 2021 after police raids and the arrests of its senior editors.

He did not opt to testify in any of his five previous cases, all of which resulted in convictions, including for organising and participating in marches during the 2019 protests.

A meeting between Lai and former US vice president Mike Pence in 2019 -- at the height of the Hong Kong protests -- has become key to the prosecutors' case to prove Lai's foreign collusion.

On Thursday, Pence took part in a Hong Kong event organised by UBS bank for its clients, where he gave "an insider view into the US elections and its far-reaching global implications", according to the event website.