The final gap between Geosan and Gunseon was closed on 1 September 1928, completing the line in its entirety from Wonsan to Hoeryeong. At the same time, the line was split, with the Wonsan−Cheongjin section being named the Hamgyeong Main Line, and the Cheongjin−Hoeryeong section becoming the Cheongjin Line. These lines later played a major role in the Japanese invasion of Manchuria, and grew further in importance after the establishment of the puppet state of Manchukuo.