"The president interceding in my father's case will show Xi Jinping how much of a mistake it is, the persecution of my father," Sebastien Lai told AFP in London, where he lives.

"If he dies, many countries will be rightfully outraged, but also," he said, "there's no upside to what they're doing."

The elder Lai founded the now-defunct Apple Daily newspaper which campaigned for democracy in the financial hub which Britain returned to China in 1997.

He was found guilty of collusion with foreign countries under a harsh security law imposed by Beijing in 2020 after it crushed massive pro-democracy protests.

His son said that the 20-year term was effectively a "death sentence" for his father, who is 78 and has faced a series of health problems.

"The Hong Kong government has essentially decided to destroy their greatest asset -- their legal system -- in order to vindictively go after my father," he said.

The tycoon is "a man who has committed no crime, a man who over the last few years and multiple show trials where they have found nothing -- the only thing they came up with is this vague idea of colluding with foreign forces".

Trump has previously said he hopes to visit China in April, although no date has been confirmed.

While running for election, Trump had vowed to secure the release of Lai, who enjoys wide support in Washington both among democracy and media rights activists and among Christian groups as Lai is a devout Catholic.

The sentence of Lai, who only holds a British passport, comes little more than a week after British Prime Minister Keir Starmer visited Beijing.

"A lot more can be done," Starmer said of Britain's efforts on his father.

"There is a real test in this relationship. If they're not even willing to release my father, to put a 78-year-old man who's in very bad health on a plane," he said, "then it tells you all you need to know."