Trains are categorized by speed service In China. Different letters indicate different types of the train, including G, D, C, Z, T and K. The trains numbers with letter G, D or C are high-speed trains.
C-class (for Chengji, simplified Chinese: 城际列车) trains are also called intercity high-speed rails which are running frequently between two not-so-distant cities with speeds of 200 - 250 km/h. Usually, the journey will not exceed 2 hours, for example, C-class trains on the Beijing - Tianjin - Tanggu line, Guangzhou - Zhuhai line.
Because C-class train speeds are lower than G-class trains, its ticket prices also are cheaper, like D-class train.