China has imposed a massive news blackout on the deadly police suppression of a village protest in Dongzhou earlier this month.

China's state controlled media have been nearly silent about the December 6 incident in which activists say some 20 people were shot dead by police while protesting against a local power plant.

The only official news coverage has alleged that three civilians were killed and several injured after protesters attacked police, forcing officers to respond.

The news blackout extends to the Internet, where reporters say sophisticated filtering has blocked foreign news stories and prevented search engines, such as Google, from looking for keywords associated with the shootings.

But media rights group Reporters without Borders says some Internet users have successfully published messages about the incident in chat rooms by alluding to the shootings without mentioning specifics.