Former media tycoon Jimmy Lai on Tuesday pleaded not guilty to collusion and sedition charges laid against him in his national security trial, with prosecutors laying out opening arguments in the High Court case.

Lai, founder of the now-defunct Apple Daily, faces two conspiracy charges of collusion of foreign forces, including by allegedly calling for international sanctions against China and the Hong Kong SAR. He's also accused of conspiring to publish seditious publications.

On the fourth day of the hearing held at the West Kowloon Court, Lai pleaded not guilty to each of the three charges laid out. Represented by a separate legal team, three firms linked to the now-defunct outlet also pleaded not guilty to similar charges.

In his opening statement, government prosecutor Anthony Chau said the prosecution will rely on evidence by witnesses and messaging records to show that Lai was the “mastermind” of a syndicate, noting that he had pursued his political agenda during the 2019 protests.

Calling him a "radical political figure", the prosecutor pointed out that Lai met with foreign politicians in 2019, including then-US secretary of state Mike Pompeo.

Chau said the former media tycoon allegedly conspired with others to call on a number of foreign countries to impose sanctions on China and Hong Kong, adding some individuals had acted as agents and intermediaries receiving information and instructions from Lai.

Prosecutors presented a colour-coded chart on an overhead projector screen said to be Lai’s “external political connections” in places such as the US, the UK and Taiwan.

Chau alleged that even before the national security law came into effect, the former media tycoon had already been actively requesting foreign forces to target Chinese and Hong Kong officials.

The prosecution also noted that 31 of the 161 articles deemed seditious, and published by Apple Daily during the duration of the alleged conspiracy, came out after the promulgation of the national security law in 2020, which included calls for the US to impose sanctions on the Chinese and SAR governments.

The court was also shown a number of social media posts by Lai and interviews he did with various outlets and organisations in which he suggested imposing sanctions.

In one of the posts, Lai asked if sanctions should be imposed on a group of people in a photo holding a banner that read “Support national security legislation, defend One Country, Two Systems”.

And in a snippet of a Bloomberg interview played in court, Lai was quoted as saying Hong Kong’s “only salvation” would be for then-US president Donald Trump to impose "draconian" sanctions, and doing so would make the Chinese government hesitate to impose the national security law.

The prosecution will continue presenting its opening statement on Wednesday.

Expert and accomplice witnesses are expected to be called to testify in the trial set to last for 80 days.