Authorities in Hong Kong have arrested a man who went to board a flight out of the city, charging him with "sedition" under colonial-era laws for wearing a T-shirt with a banned protest slogan printed on it, after questioning a lone protester holding up a blank sheet of paper at the weekend.

Acting on a tip-off, national security police arrested Chu Kai-poon, 26, as he approached his boarding gate, charging him with "committing one or more acts with seditious intent," "possession of seditious publications" and "possessing other people's ID cards."

According to a government statement, somebody reported a man at the airport to police for wearing a shirt emblazoned with the banned 2019 protest slogan, “Free Hong Kong, Revolution Now!” and “Independence for Hong Kong,” as well as a “Free Hong Kong” flag, according to several media reports.

The arrest is the latest in a string of “sedition” cases in Hong Kong, which carry a maximum penalty of two years’ imprisonment, and are used alongside a draconian national security law to target peaceful criticism of the authorities.

In July 2021, a court jailed motorcyclist Tong Ying-kit for nine years for “terrorism” and “secession” under the National Security Law, after he flew the “Free Hong Kong” slogan from his bike during a street protest.

"Police received a report that a man was allegedly wearing a shirt with seditious wordings at the Hong Kong International Airport," the Nov. 29 government statement said.

"Police officers sped to the scene and further seized some flags and clothing with seditious wording, as well as an identity card relating to another person from his personal belongings."

Lone protester

Chu's arrest came after police questioned a lone protester on Sunday after he stood on the street outside the Sogo Department Store in Causeway Bay holding up a sheet of white paper, marking the anniversary of the 2022 "white paper" movement.

The man stood there for some 30 minutes before he was approached by police, during which time some passersby were overheard asking him what he was doing, the independent InMediaHK news website reported.

Police then turned up and searched the man, checking his ID and asking if he was alone.

"What do you mean by this demonstration?" they asked him, according to bystanders interviewed in the report.

"Don't you know that a blank sheet of paper could easily incite others?" they asked.

Police later confirmed the incident to InMediaHK and said the 21-year-old man, surnamed Chan, had been allowed to leave with a warning.

'High-pressure environment'

Taiwan-based Hong Kong activist Fu Tong said the crackdown on public dissent is still making his home city "a high-pressure environment" for any form of peaceful activism.

"People dare not have anything to do with protest in the current high-pressure environment of Hong Kong," Fu said. "It's inspiring that there are still people willing to stand up."

"Those of us outside the Great Firewall sometimes feel that we're fighting in vain, and it's a form of mutual comfort and support to see that there are still people in Hong Kong who persist," he said. "It encourages us to keep up the fight."

U.S.-based political commentator Hu Ping said a lone protest – like that of the Beijing “Bridge Man” in 2022 – has a profound kind of symbolic power.

"The fact that a man in black held up a blank sheet of paper on the anniversary of the White Paper Movement carries deep political meaning," Hu said. "[It] expresses an overall sense of dissatisfaction and protest."

"Some people are still willing to stand up ... despite the high level of political pressure under the Chinese Communist Party's introduction of the National Security Law in Hong Kong," he said.

Zhuang Jiaying, associate professor of political science at the National University of Singapore, said the white paper incident showed how widespread such sentiments are, despite huge government attempts to stamp out any form of protest.

"The White Paper Revolution took place under the Chinese Communist Party's high-pressure, zero-COVID environment," Zhuang said. "While the [authorities] were able to suppress it very quickly and completely, they can't entirely eradicate sporadic protests."

"Even Beijing has no way to prevent such things, so I don't think it's surprising that such incidents happen from time to time in Hong Kong," he said.