The Chosen Government Railway (Sentetsu) nationalised the privately owned Tomun Railway on 1 April 1929, acquiring the private railway's route from Hoeryŏng to Tonggwanjin (now Kangalli) and calling it the "West Tomun Line".

[2] Intending to create as short a route as possible from Japan to Manchuria, Sentetsu had started building its own "East Tomun Line" from Unggi (now Sŏnbong) towards Tonggwanjin in 1929, eventually reaching Namyang on 1 December 1932, and finally closed the final gap between Namyang and Tonggwanjin on 1 August 1933, thus completing the Tomun Line from Hoeryŏng to Unggi; Tonggwanjin station was renamed Tonggwan at that time.

This established the desired shortest-possible connection from Japan to Harbin via the Korean ports of Ch'ŏngjin and Unggi through Xinjing.

[5] The line is used for import-export traffic between the DPRK and China; the primary exports shipped through to China are magnetite, talc and steel, and the main import is coke.

[7][8] A yellow background in the "Distance" box indicates that section of the line is not electrified.