More high speed rail than the rest of the world combined, all built in the last 15 years. It's some of the fastest too, with peak speeds exceeding those in Japan (where they are limited due to noise concerns rather than safety or the capabilities of the trains).
They are also now building new maglev lines, starting in Beijing, which will be the fastest in the world, and are going to be the longest and most extensive in the world as they rapidly expand.
They also have more underground rail than the rest of the world combined, all built in the last 20 years.