Three Hong Kong democracy supporters were jailed for up to five and a half years on Friday for their involvement in a protest at the city's airport where a mainland Chinese state media reporter was tied up and assaulted.

Hong Kong was rocked by seven straight months of huge and sometimes violent democracy protests in 2019 which China has since stamped out with a crackdown.

At one point, protesters converged on and blockaded the airport for two days causing travel chaos.

During the protests, some of those in the crowd turned on two people they accused of being Chinese "spies" or undercover police.

One of those attacked was Fu Guohao, a reporter from China's mouthpiece Global Times.

His assault was broadcast live online and caused fury inside mainland China where it was seized on by authorities as a way to bolster their narrative that the protest movement was violent and chaotic.

Amy Pat, Lai Yun-long and Ho Ka-lok were all convicted of rioting and assaulting Fu. Pat was also convicted of a charge of false imprisonment for tying Fu up.

Fu Guohao, a reporter from China's mouthpiece Global Times, was attacked at Hong Kong airport by pro-democracy protesters
Fu Guohao, a reporter from China's mouthpiece Global Times, was attacked at Hong Kong airport by pro-democracy protesters AFP / Anthony WALLACE

Ho was sentenced to five and a half years in prison, Lai five years and three months, and Pat to four years and three months.

Footage of the assault showed Fu wearing a yellow journalist vest but claiming to be a tourist when he was confronted by the crowd.

He was surrounded, zip-tied, restrained on a baggage cart, kicked and punched by a group of attackers.

A t-shirt with a slogan supporting Hong Kong's police was found in his backpack and displayed with Fu until volunteer medics in the crowd and then an ambulance crew eventually got to him.

On the Chinese mainland, Fu was hailed as a hero on social media. A comment he gave his assailants -- "I support Hong Kong police. You can beat me up now" -- went viral.

The Global Times is one of China's most aggressively nationalist state-run papers, frequently penning scathing reports of Hong Kong's democracy movement and embracing the subsequent crackdown.

The media on the authoritarian mainland is strictly controlled by the government.