Fears that a missing Christian human rights lawyer in China may have been tortured into making a confession to trumped-up crimes have been raised by campaigners calling for his release.

Jiang Tianyong, 45, went missing on November 21 after visiting the wife of an imprisoned lawyer, persecution charity Release International reports.

He was first held in so-called 'black jail'; an unregistered detention centre with no legal status. Watchdog China Aid has noted that torture is common in these centres, and inmates are refused physical, written or verbal communication with family members or legal representatives.

Chinese authorities claim to have released Jiang, but his family have not been told where he is. According to state media, he is accused of being "in possession of documents containing state secrets" and "illegally handed over state secrets abroad".

China's Legal Daily said Jiang had "confessed to the crimes". But the UN said his disappearance could be linked to a meeting he had with UN officials in August and warned that he may be at risk of torture. Jiang's wife and Releases' partners on the ground believe he may have already been tortured into making a false confession.

Release is therefore calling on China to declare where Jiang is being held, and to give reassurance that he is not being tortured.

Jiang is the latest in a line of human rights lawyers to have 'disappeared' in China, which has been clamping down on attorneys for the past five years.

Since July 2015, more than 230 human rights lawyers and activists have been detained, and state-controlled media has branded them corrupt and criminal.

"Forced confessions are common, and in the case of Christian lawyers, often extracted under extreme intimidation and torture," said Paul Robinson, chief executive of Release International.

"Jiang has courageously stood up in the courts to call for justice. He has worked lawfully within the Chinese legal system at great risk to himself. What does this say about a nation when it kidnaps, intimidates and even tortures its human rights lawyers?

"Release calls on China to disclose where Jiang is being held, to allow him legal representation and to assure the international community that he is not being tortured into making a false confession."

It is not the first time Jiang has been detained by Chinese authorities. He was first 'disappeared' in 2011, and had previously predicted that he would be arrested for his work.

"It's deeply worrying to see a nation such as China rounding up its lawyers, and claiming it is doing so to uphold the rule of law," Robinson said.

"As a growing world power, China should embrace, rather than oppose, those who stand up for justice and righteousness under the law."

Many of the Christian lawyers who have been detained have worked on behalf of churches demolished under the Chinese government's three-year 'Three Rectifications and One Demolition' campaign, which has seen up to 1,700 churches bulldozed or had their crosses removed.

The campaign supposedly has the aim of exposing and removing "illegal structures", but is widely seen as a move to combat the increasing influence of Christianity in the country.