A prominent Christian human rights lawyer in China has disappeared after being summoned to a police station, according to the charity China Aid.

Zhang Kai, who had represented 100 churches resisting the cross removal campaign in China, was imprisoned in 2015 and then released on bail earlier this year after he "confessd" on television to disturbing public order and endangering state secrets.

He was ordered to return to a police station in Hohhot, Inner Mongolia on 27 December. He was taken into custody and both his mother and sister then received visits from securty officials who told them his release depended on his willingness to cooperate.

His mother told China Aid that security services had been to her and her daughter's homes to have a "conversation". She said: "They urged us to persuade Zhang Kai to keep quiet and cooperate with them. Whether Zhang Kai can go home or not depends on his attitude.

"Our family is in the midst of waiting anxiously. I hope Zhang Kai returns safely. Please pay urgent attention."

Bob Fu, founder and president of China Aid and a friend of Zhang, has described him as a "bold human rights lawyer".

Meanwhile, China Aid is also reporting that a trial has been held in secret for a prominent pastor in China's central Guizhou province.

The trial began on Boxing Day. Yang Hua, a pastor from Huoshi Church, is charged with "divulging state secrets".

China currently ranks 33 on the Open Doors persecution watch list but could move higher when the update on the list is published in January. Open Doors reports: "Church meetings are disrupted or stopped, and Christian lawyers defending churches from having their crosses forcibly removed have been imprisoned. Foreign influence in the fast-increasing Christian minority is seen as a threat to the Chinese government's nationalistic control."