A policeman, with his gun drawn yells warnings to protesters as they restrain arrested protesters. in Wong Tai Sin, Hong Kong, China, in 2019. Photo: AFP

A prominent Hong Kong activist was among 12 people caught by China Coast Guard fleeing the city on a speedboat heading for Taiwan, police in the city said Friday.

Andy Li, who was arrested for alleged collusion with foreign forces and money laundering in a police swoop on August 10, was detained in mainland China on suspicion of “unlawfully crossing the border”, along with others caught on the boat, the South China Morning Post reported.

The coastguard announced on Wednesday that its Guangdong force had intercepted a vessel on Sunday morning in Chinese waters off southeastern Hong Kong.

It was understood that at least one of the others on the boat had been arrested in Hong Kong over the months-long social unrest that broke out in June last year.

The pro-Beijing Wen Wei Po newspaper, citing unnamed sources, said others onboard included several arrested for their part in the sometimes violent pro-democracy protests that wracked Hong Kong for much of 2019.

Hong Kong police chief Chris Tang Ping-keung told SCMP that he did not have further details of the case, but stressed it was not a joint operation. “We are actively asking about the relevant information,” he said.

Under mainland law, illegal immigrants can be sentenced to up to one year in jail, before being expatriated.

Tang said if a Hongkonger was arrested by mainland agencies for illegally smuggling themselves across the border, the authorities there could first handle the suspects under their own law and notify Hong Kong under an established mechanism.

“If these suspects are also wanted in Hong Kong, then we will follow the mechanism to see how to hand them over to us. But I do not have information on individual cases,” he added.

Beijing imposed its swingeing national security law in June after tiring of the protests.

Overnight, certain opinions and expressions in previously free-wheeling Hong Kong became illegal, and activists have spoken of a deep chilling effect that has seen books yanked from libraries and publishers rush to amend their titles.

Hong Kong’s administration insists the law has not impinged on the rights to freedom of speech and assembly guaranteed to the territory when it returned to Chinese rule in 1997.

But a number of pro-democracy figures have left the city since it came into effect, fearful that they may be swept up in a Beijing dragnet and disappear into the mainland’s opaque and Communist Party-run justice system.

Before the new law was imposed in response to the huge protests that erupted in June 2019, Hong Kong police had arrested more than 9,000 people, among whom more than 600 were charged with rioting, which carries a maximum penalty of 10 years in jail.

At least 50 former Hong Kong protesters had already applied for asylum in various jurisdictions before the coronavirus pandemic ended most international travel. Hundreds more have relocated to democratic Taiwan.

Hong Kong police said the 12, aged between 16 and 33, were being held by mainland authorities.

They gave no details on when they would be handed back to Hong Kong.