A court in northern China is trying the first of four human rights advocates charged with subversion of state power after being arrested last year in a sweeping crackdown.

The official Xinhua news agency said Tuesday that a trial had begun for the activist Zhai Yanmin, who was arrested last July as part of a countrywide government campaign against lawyers and activists. Prosecutors announced last month they would try a lawyer and three activists including Zhai. More than a dozen others remain jailed, their legal status uncertain.

Xinhua said the trial would be open and attended by five foreign media outlets and other observers. Police cordoned off the Tianjin No 2 Intermediate People's Court on Tuesday, one day after protesters flanked by foreign diplomats demanded more information about the cases.