The fast trains are called '''CRH''', China Railway High-speed. At some train stations. there is a separate CRH ticket office; at others, CRH tickets are sold at separate counters in the main ticket office. In either case, just look for the "CRH" signs. There are just two classes, unsurprisingly named first and second. Prices are not all that different, for example 69 vs 88 for Nanjing-Suzhou. Nor are the classes all that different, though first has noticeably wider seats.
Train numbers for these trains all start with "C" or "D". Intermediate-speed trains have a "Z" or "T" prefix, the slower and more crowded ones generally have "K", "N" or no letter.
Top speed on some of the recently built lines, like Beijing-Tianjing, is 350 km/h (nearly 220 mph). Older major lines, like Nanjing-Shanghai-Hangzhou, top out at 250 km/h (150 mph). Other lines are limited to 160 or 200 km/h (about 100 or 125 mph).
See China#Get_around for more general information on rail travel in China.
Several of those lines are being upgraded and new lines are under construction:
When all is complete, Beijing - Shanghai travel time will be cut to five hours and Guangzhou-Beijing to twelve.
There will also be a line running North-South along the coast, Guangzhou - Shantou - Xiamen - Hangzhou - Shanghai.
Shanghai has a '''magnetic levitation''' train out to Pudong airport. Top speed is around 431 km/h (268 mph) during daytime and 300 km/h (186 mph) in early morning or after 5pm.
A maglev line between Shanghai and Hangzhou has been planned, but construction has not started. There are rumours the project has been cancelled, but the Shanghai government denies them.