For the last 20 years, CBN News has documented the explosive growth in China's so-called underground or house church movement, as millions in this officially atheistic nation converted to Christianity.

From 24-hour prayer services to the powerful move of God in China's vast countryside, this reporter has crisscrossed the nation chronicling the stories of lives transformed by the preaching of the gospel going back to the early 1990s.

Experts say what's been happening in China is part of an unprecedented religious revival that has touched every corner of the country, leading some to predict that China could become the world's most Christian nation by 2030.

But China's President Xi Jinping wants to prevent that. Since taking power in 2012, Xi has ordered authorities to shut down any house church not under Communist government control, leading to what one expert says has been a "massive new wave of persecution" sweeping the nation.

Bob Fu, with US-based ChinaAid, is documenting the widespread crackdown.

"I'm talking about hundreds of thousands of churches were shut down, pastors were being arrested and prayer meetings were being raided," Fu said.

Pastor Jin Mingri knows harsh tactics firsthand.

In August, Jin, who led Zion Church, the largest unregistered congregation in Beijing, refused a government order to install closed-circuit surveillance cameras in the sanctuary.

"A lot of our flock are terrified by the pressure that the government is putting on them," Jin said. "It's painful to think that in our own country's capital, we must pay so dearly just to practice our faith."

Weeks later, authorities outlawed the 1,500 member church and banned him from preaching.

"It's probably the largest incident of the government using public power to apply pressure on a house church in the past ten years, and it is still going on today," warned Jin.

And it's not just happening to big congregations.

Several men, led by a local official, forced their way into 63-year-old Xu Shijuan's tiny apartment in Henan province, then ordered her and two dozen elderly Christians to stop meeting for Bible studies.

Xu, like the majority of China's Christians, insists her faith is not a threat to the government or country.

"Christians pray for the country and for the people, hoping that our country will become better, prosperous and strong," Xu insisted.

Bob Fu says the crackdown is part of President Xi's ambition of "Sinicizing" Christianity with "Chinese characteristics" and insisting that Christians pledge political loyalty to him and the Communist Party.

In April, the government's religious affairs bureau headed by Xi said all churches must embrace the new party ideology, insisting that "only Sinicized churches can obtain God's love."

"He is really wanting to take China to the Chairman Mao's old kind of path by exercising more political control, mind control, ideological kind of "sinicization" into the Communist Party's ideology," worries Fu.

Andrew Nathan of Columbia University says the government views Chinese Christians like dry kindling that could spark a political uprising against the government, with the help of outside influence.

"They think that foreign forces, the United States, missionaries and so forth, will like to spark up this tinder," Nathan, a political science professor at the university said. "They don't see it only in a domestic context, they see it in a strategic context as well."

As authorities tear down crosses, burn Bibles and replace images of Jesus Christ with posters of the Chinese president, Wang Yi, one of China's most prominent pastors arrested this month, boldly declared that Xi's god-like status was "incompatible" with the Christian faith.

His church was shut down and more than 100 members of his congregation arrested.

Foreseeing his possible arrest, pastor Wang wrote a letter titled "My Declaration of Faithful Disobedience" with instructions that it should be published if he went missing for more than 48 hours.

In it, Wang vowed to use non-violent methods to stand against Chinese laws he believed were against the Bible and God.

Read Pastor Wang Yi's full letter here.

Now, after years of enjoying relative freedom from government interference, Christians like one woman whose husband is under house arrest and wants to remain anonymous, worries about the future climate for China's Christians.

"It's painful," the Christian woman said. "The government says that we have religious freedom, but really there is no freedom at all." Xu, who remembers vividly what life was like for Christians under Chairman Mao's repressive rule, has complied with authorities and stopped the meetings.

But says: "Our faith has not stopped. God's path cannot be blocked. The more you try to control it, the more it will grow."