Hong Kong authorities charged a 26-year-old man with sedition on Wednesday after police allegedly found "seditious wording" on a shirt he wore and on flags in his possession.
China has tightened its grip on Hong Kong after the finance hub was rocked by huge and sometimes violent pro-democracy protests in 2019.
The following year Beijing imposed a sweeping national security law on the city to quell dissent. Local authorities have also revived a long-dormant sedition offence left over from British colonial rule.
Appearing in court on Wednesday, the man was denied bail after being charged with one count of committing an act "with seditious intention" and one count of "possessing seditious publications".
Hong Kong police said it received a report on Monday afternoon that "a man was allegedly wearing a shirt with seditious wordings at the Hong Kong International Airport", without naming him or specifying what was written on his belongings.
"Officers sped to the scene and further seized some flags and clothing with seditious wording," police said in a statement.
More than 30 people in Hong Kong -- many of whom are not activists and have no public profile -- have been charged with sedition since the 2019 protests were crushed.
First-time offenders face up to two years in jail.
In September, China mulled new legislation to ban clothing that "hurt the feelings" of the Chinese people.
The draft law, released for public consultation that month, sparked backlash on Chinese social media, with users fearing its vagueness left it open to broad interpretation and enforcement.
On Wednesday, Hong Kong prosecutors also charged the man with a separate offence related to the possession of an identity card that did not belong to him.
The case was adjourned until January 4 to allow time for prosecutors to search the man's phone and social media, according to Hong Kong media reports.