Jimmy Lai, Hong Kong's pro-democracy media tycoon, has been jailed for 20 years for colluding with foreign forces under the city's controversial national security law.

Rights groups called it a death sentence for the 78-year-old, whose family has raised concerns about his health, but Hong Kong's leader said it was deeply gratifying.

This is the harshest punishment to be handed down under the law, which China imposed after huge protests in 2019 demanding more freedom, and defends as essential for the city's stability.

Lai, a British citizen, is the most prominent of the hundreds arrested under the law. A fierce critic of China, he often wielded his paper, Apple Daily, as a tool of protest.

It is incredibly heartbreaking, Lai's son, Sebastien, told the BBC's Today programme, adding that he had repeatedly raised Lai's imprisonment with the UK government but obviously my father is still in prison.

Six former Apple Daily executives and two activists were also sentenced on Monday under the national security law, with terms ranging from six years and three months to 10 years.

Human rights advocates condemned the decision as a devastating blow to press freedom, with the Committee to Protect Journalists calling it the final nail in the coffin for independent journalism in Hong Kong.

Despite international outcry, China's foreign ministry dismissed criticisms as interference in what they claim are internal affairs.

Lai's case highlights the ongoing tensions between Hong Kong's push for democratic freedoms and the stringent measures imposed by Beijing to quash dissent.