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

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

Lai's legal team told AFP they would not provide an explanation for the decision to not appeal.

Rights groups have condemned his punishment as "effectively a death sentence" and a symbol of the city's shrivelling press freedoms.

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

Meanwhile, Hong Kong's leader John Lee lauded the "severe" 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.