Christian congregations in North Korea are typically made up of two or three people from the same family.
According to Voice of the Martyrs (VOM), the church has had to go deeply underground under the Kim Jong-un regime.
People may face the death penalty or detention if their faith is discovered.
Voice of the Martyrs (VOM) spokesman Todd Nettleton has told Fox News, the regime teaches that its leaders are divine beings, not just political or authoritarian figures.
Mr Nettleton says that in the eyes of the North Korean government, Christianity amounts to treason, because if Jesus is Lord, then by defiinition, Kim Jong-un isn’t.
Christianity is seen as so dangerous to the regime that it simply cannot be allowed to spread inside the country.