China's most prominent liberal philosopher is defying demands by the Communist Party to retract his signature from a ground-breaking call for reform, elections and freedom of speech that has infuriated the government.

Police and Party officials have threatened and harassed more than 100 of the 300 leading intellectuals, lawyers and activists who signed Charter 08, a call for a new politics consciously modeled on dissident movements in the former Soviet bloc.

The Charter's alleged organiser was taken from his home shortly before the document was launched on the 60th anniversary of the United Nations Declaration of Human Rights last month, and is still being held.