It's not exactly a secret that the official Chinese government statistics are often made up or obfuscated. The official stats for road network length say 4,696,300 km of roads. According to the CIA world factbook, China has 4,046,300 km of paved roads. In 2016, on OSM 1,635,931 km of roads was mapped in China. Update: in June 2017 we're already at 2,022,047 km!
Pretty much all unclassified roads are still missing from OSM, and this is the case for most of rural China. Even for cities, there are only a handful of cities that have their residential roads mapped well. So it leaves me wondering, is the 4 million km of roads in total a realistic statistic?
Looking at the satellite imagery again, there are (minor) roads in a grid of about 300 meters distance. The densely populated North China Plain alone has an area of 409,500 km². Assuming every squared km of this area is covered by 6 km of roads, then there is a total of almost 2,500,000 km of roads in the Northeast China Plain alone. Within villages, the road grid is much more dense. And of course there are plenty of other densely populated areas in China, such as the Sichuan Basin, the Loess Plateau, the Northeast China Plain, the Pearl River Delta etc. etc.
Doing some very rough calculations (area of above regions times 2 km of road per square km):
Is it doubtful that the rest of the country has only 1.3 million km of roads? And this is with a conservative estimate of 2 km of roads per square km (although the Loess Plateau is not that densely populated).
There is also the number of road length per capita. It seems Germany has a comparable population density to China (the population of Western China is neglible). Using the number from Germany (2.81) times the population of China gives around 4,000,000 km of roads. Comparable to the official stats.
The only way to get the answer is by waiting some years for the OSM data to grow further. It's actually likely that even the Chinese government doesn't know the real number, as maps used in China (Baidu, Tencent) lack most of the minor roads. It could be that they censor it, but the purpose seems unclear in that case.