An imprisoned Chinese pastor has urged his wife to hold on to faith and trust God in a moving letter sent from his detention centre.

Pastor Li Guozhi, also known as Yang Hua, was arrested more than six months ago by Chinese authorities and is now being held in Nanming district.

He leads a house church in China's central Guizhou province.

"You shouldn't be too anxious. It is best to remain peaceful and wait for God," Li said in the letter to Wang Hongwu, sent June 6 and translated by Christian charity China Aid.

"God is omniscient. I believe that he never makes a mistake... Let's pray and leave other things to God. Thank you for investing everything in this family. I am grateful for what God has given me; let's carry the cross and hasten down the road to heaven, until the day we meet the Lord."

Li requested a recent photo of their sons and says he's "adjusted" to life in detention.

"As the Book of Isaiah says, 'In repentance and rest is your salvation, in quietness and trust is your strength' [Isaiah 30:15]. It's also a kind of rest, staying inside."

He ends the letter by encouraging Wang to "always be happy and peaceful. Never stop praying. Be grateful, because that's God's will conveyed through Jesus Christ."

Wang previously told Radio Free Asia that Li has been denied permission to meet with his lawyer while detained.

He faces charges of "deliberately leaking state secrets".

The Chinese government has been taking an increasing hard line on religion, particularly against Christianity which is experiencing dramatic growth in the country. More than 1,500 churches have been demolished or had their crosses removed in Zhejiang province over the past three years, and pastors and lawyers who opposed the campaign have been imprisoned on charges widely regarded as concocted by the authorities.