Authorities in Hong Kong arrested a veteran rights activist known for carrying coffins at protests for "subversion," after he announced he would protest outside the ruling Chinese Communist Party (CCP)'s Central Liaison Office in the city on the first day of the 2022 Beijing Winter Olympics on Friday.

Koo Sze Yiu, 75, was arrested under a draconian national security law imposed on Hong Kong by the CCP, on suspicion of "incitement to subvert state power," a charge that carried a maximum penalty of life imprisonment.

He was arrested by national security police at 6.00 a.m., and is being held at Cheung Sha Wan police station for questioning, local media reported.

Police also brought in four fellow activists for questioning in connection with Koo's case, including veteran activist Lui Yuk-lin.

Koo was a colorful and regular feature of the regular and peaceful mass protests that once took place regularly in Hong Kong, before a city-wide crackdown on "illegal" public assembly in the wake of the 2019 protest movement.

Koo, who has stage four colorectal cancer, has been arrested and jailed several times already since the 1997 handover of Hong Kong, including for "desecrating the national flag" in July 2020.

Meanwhile, more than 10 police vehicles and dozens of uniformed and plainclothes officers were deployed outside Beijing's liaison office, with roadblocks on the approaches to the building on Des Voeux Road West and Connaught Road West.

Many bore armbands delineating them as "Special Police," including fire department and immigration officers.

Koo's arrest came after he issued a news release on Thursday announcing his plan to protest outside the Central Liaison Office on Friday, "raising and sending off a coffin to celebrate the Winter Olympics ... and the national security law."

League of Social Democrats (LSD) spokesman Dickson Chau said he had no idea the arrest would take place.

"[This shows that] they don't just expect Hong Kong to take the same strict COVID-19 prevention measures as the rest of China; they also want zero leniency when it comes to dissidents," Chau told RFA.

"This is a higher-level of stability maintenance and a higher-level alert," he said.

He said the next six months would likely see no let-up.

"We have Xi Jinping seeking a third term and the 25th anniversary of Hong Kong's return to China," he said. "Dissenting voices will definitely be eliminated."

Opinion pollster Chung Kim-wah said a political boycott of the Olympics over the CCP's rights record in Xinjiang, Tibet and Hong Kong, as well as its growing military threats against the democratic island of Taiwan, had made the Olympics a "much more sensitive international issue."

"Beijing is in an embarrassing situation with this Winter Olympics, because so many countries are staging political boycotts," Chung told RFA. "I think the Hong Kong government is working right along with those concerns in Beijing, and so they won't tolerate any negative voices on the subject."

"[That's why] they are taking decisive action against Koo, as a deterrent, to act as a clear warning to people not to try anything in the next couple of weeks," he said.

Meanwhile, hundreds of Hong Kong protesters and rights campaigners took to the streets of central London on Thursday night to call for sanctions against Chinese and Hong Kong officials responsible for rights abuses in Hong Kong, including the city's leader, Carrie Lam.

Shouting "Shame on China! Free Tibet! Free East Turkestan! Free Hong Kong!" the protesters staged an "alternative" Olympics opening ceremony at Picadilly Circus, some of them dressed as Winnie the Pooh, in a satirical dig at Xi Jinping, while others brought effigies of tanks and the Olympic five rings, and others played out a sketch in which International Olympics Committee president Thomas Bach presented a gold medal to Xi for "human rights violations."

Ruling Conservative Party member Nusrat Ghani, who has been sanctioned by Beijing for speaking out against the mass incarceration of Uyghurs in Xinjiang, warned that the CCP will use the Winter Olympics to "whitewash evil deeds", and called on the international community to take notice of the repression suffered by Hong Kong, the persecution of Tibetans, and the genocide of Uyghurs.

"No one can deny what is happening against the Uyghur people. The crime of all crimes: genocide," she said. "No to the genocide Olympic Games!"

MP Lord Alton told the rally, to cheers: "We have to sanction those who have committed these crimes, whether in Xinjiang or Hong Kong. I have Carrie Lam on my list. Sanction Carrie Lam!"