To echo what @mike.m.lin is saying, you're in for a rough ride.
VPN usage is popular for information workers to access non-Chinese resources, so that 'friction' is sort of understood and accepted within their society. However, the current state of VPNs in China is a game of cat and mouse. The Chinese government has started cracking down on VPN usage because they can't inspect the traffic, so VPN resources of yesterday get blocked, new ones spring up, and the game continues. If there's a way to develop a browser plugin that will tunnel traffic (via VPN or other) to make your application work, that will be probably the best course of action in the short term.
But that only is half the battle. Your other challenge is latency. Assuming your service is centrally hosted for your app, you'll obviously want to host it as close to the end user as possible. A common 'shortcut' is hosting it in HK as geographically that is close to China. Unfortunately it's not that simple. HK is not inside the GFW and so the performance hit is still very real. The best performance will require you actually being hosted inside China, which comes with a series of challenges and headaches.
First you'll need to decide where you want to be hosted and how that host's performance operates with respect to the rat's nest that is China's congested infrastructure. Depending on the scale of how big you need, will determine if you're dealing with Co-loc providers vs. hosting companies. Also understand that internet performance varies heavily by province. So truly getting predictable behavior within China will likely be prohibitively expensive, especially on mobile. In the last year I've know of people that get mobile broadband speeds of 100Kbps or less.
Get ready to submit source code to be inspected by the Ministry of Industry & Information Technology to obtain a license which is required by most hosting companies to even consider hosting your application in China. You'll have to rip out any code traces that tie to Google, Facebook or any other company the Chinese government has taken issue with in terms of information compliance. Example, if you have Google Analytics code in your app, and a stateful packet inspection via the GFW shows your traffic is going to domains that are 'black listed' your app will have serious issues functioning, if at all.
Furthermore, you'll need to have a native Chinese speaker representative in China to help move things along. The licensing process of getting approved to host your application in China can often take 6 months.
Moving to China has gotten easier, but it's still a serious issue and not one that you should do internally IMO. I recommend you find someone that's done it before that has presence in China to help you navigate these waters, and make sure you have an internal resource that is very network savvy to understand the realities of what you're about to embark upon. If this resource has no knowledge of BGP, ASNs, or routing/peering, they are not the right resource.
For reference here's a good blog post that gives you an idea of what may be in store Cloudflare in China