HONG KONG (REUTERS).- A spate of graffiti appearing across Hong Kong in recent weeks in support of detained Chinese artist Ai Weiwei has sparked a warning by the Chinese army garrison in the city, a newspaper reported on Saturday.

An artist in the former British colony calling himself Cpak Ming recently projected an image bearing the words "Who's Afraid of Ai Weiwei?" onto a wall at the People's Liberation Army (PLA) harbor-front barracks in the heart of the city.

While the brief artistic stunt with a camera, that was photographed and uploaded onto Facebook, left no physical trace, a PLA spokesman in Hong Kong said such acts breached Hong Kong laws and the PLA would "reserve its legal rights" to act, the South China Morning Post reported.

"No one can paint or project pictures and images onto the outer wall of the barracks with the garrison's permission. Such an offence is a breach of Hong Kong law. The PLA reserve its legal rights," the PLA spokesman was quoted as saying.

Ai, a globally acclaimed avant-garde artist and rights activist has been detained for almost one month for alleged though unspecified economic crimes, as part of a crackdown by jittery Chinese authorities fearing possible contagion from Middle East uprisings against autocratic regimes.

Besides the so-called flash graffiti beamed onto prominent buildings in Hong Kong, a rash of pro-Ai images has also been spray-painted onto walls, pavements and public spaces by a group of anonymous artists, sparking a police investigation into possible criminal damage.

Critics say Hong Kong is under political pressure from Beijing to arrest the artists, potentially testing the limits of tolerance in the free-wheeling capitalist hub which was once a British colony but reverted to Chinese rule in 1997.

The Chinese army has tended to maintain a low-profile in Hong Kong which was promised a high degree of autonomy and full democracy after the 1997 handover, though its rare warning suggests the continued spate of pro-Ai protests by the city's outspoken artistic community have begun to ruffle feathers.

Some Hong Kong lawmakers, however, saw nothing wrong with the imaginatively conceived flash graffiti to protest China's harsh crackdown in recent months against government critics it fears pose a challenge to Communist Party rule.

"He is just expressing his opinion in a very short period of time and poses no permanent damage to the building," Ronny Tong, a pro-democracy lawmaker and barrister was quoted as saying. "I cannot see why it is a criminal offence."

Chinese authorities on Friday released human rights lawyer Teng Biao, a day after a visiting U.S. official in Beijing for human rights talks, denounced his secretive 70-day detention.

(Reporting by James Pomfret; Editing by Robert Birsel)