The drilling and boring work for a cluster of six tunnels of a railway in southwest China's Yunnan Province, which is a key section of the China-Myanmar international railway corridor, was completed on Sunday, marking a major milestone in the railway's construction.

After more than six years of efforts, the builders overcome many difficulties given then complex geological conditions to complete the tunnels that link Dali Bai Autonomous Prefecture with the city of Ruili on the border with Myanmar.

With a total length of 32 kilometers, it's the largest tunnel cluster on the 330-kilometer Dali-Ruili railway.

"The first calibration of the ballastless track of the super-long tunnel cluster has been completed, providing technical and empirical reference for the overall construction of the ballastless track bed," said Xu Jiqi, site leader of Dali-Ruili Railway Project Department of China Railway 12th Bureau Group Co. Ltd.

"This July, construction conditions will be ready for tasks such as beam erection and track laying, which will meet our planned target," he added.

After completion, the Dali-Ruili railway is expected to cut the train trip between Dali and Ruili by two hours and greatly improve transportation in western Yunnan.