A Chinese pastor imprisoned in so-called 'black jail' for opposing a government crackdown on Christianity has been released, activists have confirmed.

Pastor Huang Yizi, from the eastern province of Zhejiang, was formally placed under criminal detention on 12 September 2015 for "endangering national security." He was accused of "stealing, spying on, buying or illegally providing state secrets for institutions and people outside the country" and was not allowed access to a lawyer or to speak with his family.

Human rights organisation China Aid received confirmation on Friday that Huang had been freed, just under five months after his arrest.

Founder and president of China Aid, Bob Fu, told Christian Today that the pastor looks "pale and thin", and that Huang has said he was under huge pressure and threat before his release.

Huang previously served a one year sentence for leading a prayer vigil against cross demolitions in Zhejiang but was released on 1 August last year. Police had attempted to remove a cross from the roof of Sjuitou Salvation Church in July 2014, resulting in a bloody clash with members who were guarding the building.

Officers reportedly used iron batons to beat those who stood in their way, and one member of the congregation suffered a fractured skull. The cross was eventually removed from the church building.

Huang then gathered a crowd from his congregation at a government building to demand answers about the incident. He also urged other church leaders to put back crosses which had been removed from their buildings and criticised police violence on his blog. He branded the removal of church crosses an example of "severe persecution" and an "insult" to China's Christians.

He leads Fengwo Church in Wenzhou, a city dubbed the "Jerusalem of the East" for reportedly having the largest Christian community in China.

The pastor was among at least 20 Christians from Wenzhou and Jinhua, also in Zhejiang province, to be held in black jail towards the end of last year.

'Black jails' have no legal status, though the official wording states that detainees are being kept under "residential surveillance in a designed location". China Aid has noted that torture is common, and inmates are refused physical, written or verbal communication with family members or legal representatives.

"We are glad pastor Huang is released home for Chinese New Year after being arbitrarily detained for five months in a black jail," Fu said today.

"Both the previous one year criminal sentence and the past five months detention are absolutely part of political revenge against pastor Huang's public opposition against the barbaric forced demolition of crosses and his effort for organizing true Gospel mission independent of the government controlled religious body, the TSPM [Three Self Patriotic Movement].

"I call upon the Chinese higher authorities to hold accountable of those abusers of power (in its arbitrary nature of pastor Huang's detention) in Zhejiang and restore justice to pastor Huang." 

Up to 1,700 churches in Zhejiang have been demolished or had their crosses removed as part of a three-year 'Three Rectifications and One Demolition' campaign, supposedly with the aim of exposing and removing "illegal structures". However, it is widely seen as a move to combat the increasing influence of Christianity in the country.