The 77-year-old founder of the now-shut Apple Daily newspaper has been behind bars since late 2020 as his case made its way through the courts, with many Western nations and rights groups calling for his release.

Lai has contested charges of foreign collusion under the Chinese city's national security law, which Beijing imposed after Hong Kong saw huge and sometimes violent pro-democracy protests in 2019.

Judge Esther Toh said on Thursday that the court will inform parties "in good time" as to when the verdict will be delivered.

Appearing in the dock in a white shirt and tan suit jacket, Lai smiled and waved to supporters, who waved back wordlessly after courtroom staff insisted on maintaining "absolute silence".

His case involves thousands of pages of documentary evidence which may take judges months to review, a legal source told AFP.

If the tycoon is found guilty, the court will need to hear additional arguments on sentencing.

Aside from two counts of the collusion offence -- which could land him in prison for life -- Lai is also charged with "seditious publication" related to 161 articles, including op-eds under his name.

At trial, prosecutors painted him as the "mastermind" behind multiple criminal conspiracies: one involving Apple Daily executives, another involving a web of foreign connections.

The conspirators allegedly used various platforms to request Western countries to impose "sanctions, blockades or hostile actions" towards China and Hong Kong around the time of the 2019 protests.

Defence lawyers countered that Lai had no intention to continue such activities after Hong Kong's national security law took effect in June 2020.

They added that Lai, who is a British citizen, was exercising his rights, including that of free speech, without criminal intent.

- Lai 'sowed fear' -

As the trial entered its final stages, the three-judge panel -- selected from a pool of jurists hand-picked by Hong Kong's leader -- often took a dim view of the tycoon's political opinions.

"Freedom of expression is not absolute, it has limits even in Western countries," Toh said last week as she heard closing arguments.

At one point, the judge picked up on a comment Lai made in 2020 criticising Chinese President Xi Jinping for clamping down on dissent and "eliminating the Hong Kong people".

"(Lai) is sowing fear to the population and the outside world," Toh said.

Seated in the dock, Lai remained impassive and watched the evidence displayed on a screen.

The tycoon has been jailed for more than four years, reportedly in solitary confinement, and has lost weight during that time.

Throughout much of the proceedings, members of Lai's family, including his wife Teresa, observed from the public gallery.

Consular representatives from the European Union, United States, United Kingdom and other democratic nations were also frequently spotted in court.

Defence lawyers said this month that Lai had experienced heart palpitations and had an episode where he felt like he was "collapsing".

He continued to attend hearings without visible discomfort after he was prescribed medication and fitted with a heart rate monitor.