The ground-breaking ceremony took place near the city of Mary in the southeastern part of the Central Asian country, close to the giant Galkynysh gas field which is meant to provide gas for the 1,814-kilometre (1,127-mile) link.
"By December 2019, the pipeline will be completed," Turkmen President Kurbanguly Berdymukhamedov said at the ceremony.
"It will have a capacity of 33 billion cubic metres."