LOL? Never would have figured that there was religion in China at all, weren't they still Communist/People's Republic?
I'm told by a professor at a mainline Protestant seminary that, if one counts by the number of Protestants in church one any given Sunday, that mainland China is the second largest Christian nation in the world. Partially this is because of the precipitous decline in attendance traditionally Protestant European countries, partially this is because evangelical/nondenominal Protestant missions have yielded massive success there, as - perhaps more - successful than in Latin America. He estimates that around 10% of the overall population is churchgoing in this sense. This implies very large numbers - as much as 20-30% - in the cities, since I highly doubt this is a rural phenomenon.
Mainland Chinese I know generally confirm that this is massive - despite the official ban on uncontrolled church activity. Based on what I've seen in/heard from ethnic Chinese mega-churches in Singapore, Hong Kong and Taiwan, I'll also believe it. Based on those, I'd further imagine the majority of the congregants are under 30.
In fact, I recently attended a such a church, and raised an eyebrow at seeing an auditorium packed with at least 3,000 college students and professional 20-somethings reading bibles and then going to church afterward. What impressed me most is that much of the actual work is done by people of the same age - obviously there's a charismatic older pastor, and there are older folks behind the scenes, but all of the faces of the congregation (i.e. people singing, dancing or playing instruments) and many of the workers making the AV system and projectors work, as well as the group leaders, are also 20 somethings.
Even the most complacent Eastern Christian or Latin Catholic cannot but raise an eyebrow at this. I've been thinking of posting about this in the parish life/evangelization forum, but have my doubts about its relevance for us.