BEIJING—James Powderly, a New York street artist and the founder of Graffiti Research Lab, has been detained in Beijing for planning a pro-Tibet protest, as have five activists who carried out another act of protest, reports the blog Boing Boing.

Powderly's work involved projecting a pro-Tibet message using a handheld green laser with micro-stencils. The act was to be part of a series of protests organized by Students for a Free Tibet around the Olympics. Powderly had submitted the project for the internationally organized new-media art show "Synthetic Times" and decided, when it wasn't accepted, to bring it to China on his own.

The other detainees, also affiliated with Students for a Free Tibet, unfurled a banner at the Olympic Park last night that spelled out "Free Tibet" in English and Chinese in LED lights, according to a press release from the organization; within 20 seconds, the protesters were seized and detained. The whereabouts of the six protesters are unknown.