Lai, 76, has denied all charges levelled against him.

He was jailed in December 2020.

If found guilty, then he faces life in prison.

He was arrested under the National Security Law, which China has been accused of wielding to crush dissent, reported BBC.

Lai, who appeared in court on Monday flanked by prison guards, is one of more than 250 activists, lawmakers and protesters who have been detained under National Security Law (NSL) and sedition charges since 2020, the British media reported.

The trial is expected to take place for 80 days.

Lai's international legal team told the BBC he has been denied his right to a fair hearing.

Jonathan Price, a member of Lai's London-based legal team, described it as "lawfare". 

UK Foreign Secretary David Cameron reacted to the incident and posted on X: "At the start of Jimmy Lai’s national security trial in Hong Kong, I call on the Hong Kong authorities to end his prosecution and release him."

Who is Jimmy Lai?

Born in China, Lai moved to Hong Kong as a child. He is currently a British citizen.

He is the founder of Giordano, an Asian clothing retailer, Next Digital (formerly Next Media), a Hong Kong-listed media company, and the popular newspaper Apple Daily.

The Chinese government considers anyone of Chinese heritage born in China to be a Chinese national.

The Chinese government does not recognise dual nationality and therefore considers Lai to be exclusively Chinese.

The National Security Law was imposed by Beijing on 30 June 2020.

The UK declared its imposition to be a breach of the Sino-British Joint Declaration on 2 July 2020.