The 78-year-old founder of the now-defunct Apple Daily newspaper was found guilty in December on charges of foreign collusion and seditious publication.

His sentence was the harshest penalty doled out so far under a national security law imposed on Hong Kong by Beijing after widespread pro-democracy protests in 2019.

"We have clear and definitive instructions (from Lai) not to lodge an appeal against conviction or sentence," his legal team told AFP, adding that they would not give an explanation for the decision.

Lai's conviction and sentencing received international condemnation, with rights groups saying his punishment was "effectively a death sentence" and a symbol of the city's shrivelling press freedoms.

His son, Sebastien Lai, said the "draconian prison sentence is devastating for our family and life-threatening for my father".

UN rights chief Volker Turk has called for the verdict to be "promptly quashed as incompatible with international law".

US President Donald Trump, who is expected to visit China in late March, has urged China's leader Xi Jinping to free Lai.

China rejected the criticism, with Beijing saying it lodged "solemn representations" with nations that condemned the sentence.

Hong Kong's leader John Lee lauded the "severe" prison term as a demonstration of the city's rule of law.

Eight other defendants, including six Apple Daily executives, were handed jail sentences of up to 10 years in the same case. All except Lai had pleaded guilty.

Lai's decision reflects a "general disillusionment" with how the judiciary handles national security cases, said Urania Chiu, a law lecturer at Oxford Brookes University.

She said the courts have "shown a 'national security first' approach which allows no space for rights-based arguments".

"Against this backdrop, it is hard for individual defendants and the general public to place trust in the judiciary's independence and competence," Chiu told AFP.

Eric Lai, a senior fellow with the Georgetown Center for Asian Law, told AFP "it is premature to conclude whether forgoing an appeal might facilitate a negotiated release" ahead of any meeting between Trump and Xi.

That was because geopolitical conditions have "shifted considerably" with war breaking out in the Middle East.

Lai won an appeal against separate fraud charges last month related to a contractual dispute, with Hong Kong's government saying it would consider an appeal against the ruling.