Updated

Around 20 attorneys have gathered in a central Chinese city to demand access to several activists detained ahead of the politically sensitive 25th anniversary of the Tiananmen Square military suppression of protesters.

Prominent rights lawyer Li Fangping says the attorneys staged an overnight protest starting Friday outside the Zhengzhou city police bureau after authorities denied their requests to see their clients.

Among the activists detained in Zhengzhou is well-known lawyer Chang Boyang. Chang has campaigned for the rights of migrant workers, HIV patients and children poisoned in a 2008 tainted milk scandal.

He was detained May 27 as part of a string of prosecutions against artists, lawyers, scholars and journalists ahead of the June 4 Tiananmen anniversary amid intense government efforts to deter public commemorations.