"They hung me up across an iron gate, then they yanked open the gate and my whole body lifted until my chest nearly split in two. I hung like that for four hours."

That is how Peter Xu Yongze, the founder of one of the largest religious movements in China, described his treatment during one of five jail sentences on account of his belief in Christianity.

Mr Xu, 61, is not the only Chinese Christian to suffer for his faith. Both Catholics and Protestants have long complained of persecution by the Communist authorities, and human rights groups claim the problem is getting worse.

According to the Jubilee Campaign, an interdenominational lobby group, about 300 Christians are in detention in China at any one time, and that number is set to rise.

"China's new generation of leaders are trying to consolidate control of the country as it goes through rapid social and economic changes," said Wilfred Wong, a parliamentary officer for the Jubilee Campaign.

"The Communists feel threatened by any popular ideology which is different from their own," he said.

China's Christian population - especially those who refuse to worship in the tightly regulated state-registered churches - is seen as one such threat.

According to Mr Wong, the number of Christians in China has continued to rise, exacerbating this perceived threat and causing the authorities to clamp down still further on unregistered churches.

The perception that China's Christians have close links with the West adds to their plight, Mr Wong said.

'You can't evangelise'

Christianity is not actually banned in China. In fact, according to the constitution, "citizens of the People's Republic of China enjoy freedom of religious belief."

Beijing backed up that statement in 1997, saying that "In China, no one is to be punished due to their religious belief". But human rights groups and Christians say that the reality is different.

"They say you can believe, but you can't evangelise," Mr Xu said. "But that is a natural act for Christians. The bible commands us to preach the gospel."

According to Mr Xu, who has now left China and lives in the US, it is against regulations to worship in groups. He said that one of his arresting officers even told him he could only avoid breaking the law if he prayed under the covers in bed.

To an Evangelical Protestant like Mr Xu, joining one of China's state-sanctioned churches was simply not an option - and it seems many other Chinese Christians agree with him.

Getting reliable numbers about the number of Christians in China is notoriously difficult. Estimates vary between 40m to 70m Protestants, only 10 million of whom are registered members of government churches.

The situation is similar for Catholics. Of the estimated 15 to 20 million Catholics in China, less than half belong to state-approved churches, which put authority to Beijing before authority to Rome.

Those Christians who want to avoid the state-controlled religious movements meet in unofficial buildings or even each others' homes - hence their description as "house churches" - risking fines, imprisonment, torture and even, in some cases, death.

Government crackdown

Human rights groups have documented an increasing number of arrests of Chinese Christians since the beginning of 2004.

According to the charity Christian Solidarity Worldwide, persecution is becoming more systematic and targeted at large-scale Christian gatherings.

Since June the charity has documented three mass arrests of unregistered Christians. In each case more than 100 people were detained.

Amnesty International has reported many cases of detained church leaders in recent years, especially in the provinces of Zhejiang, Jiangsu and Hebei.

One of the most high-profile cases is that of Gong Shengliang, head of the South China Church, who was sentenced to death in 2001. His sentence was commuted to a prison term, but Amnesty has received reports that he has been severely tortured in jail.

In August three Christians were sentenced to jail terms for passing information to foreign governments, and in July state media reported that a woman had been beaten to death after being arrested for handing out bibles.

Peter Xu said that while he was in jail, he saw several people even being killed for their faith.

"A believer was praying, so a jailer made other prisoners lift him up to the ceiling and drop him to the ground many times until he died," Mr Xu said.

But government crackdowns - and even torture - may not make people like Peter Xu give up their faith.

"Despite all the persecution and suffering, God is calling more and more people in China," he said.