Construction of the China-Laos railway is gathering steam, as a main bridge over the Mekong River has been completed, said executives of construction giant China Railway Engineering Corp.

The rail project, which will connect Southwest China with Laos by 2021, is part of the two countries' efforts to promote interconnectivity.

Last week, a subsidiary of State-owned CREC completed the construction of the No 21 pier foundation of the Luang Prabang bridge across the Mekong River. As one of the key projects of the China-Laos railway, the bridge is 1,458.9 meters long with 34 spans.

Tang Gaoyun, a division Party secretary of the China Railway No 8 Engineering Group, said the bridge is one of the line's most difficult and complicated projects, due to the river's deep water and strong current.

The completion of the No 21 pier foundation will pave the way for future construction, Tang said.

The China-Laos railway project first kicked off in December 2016. The 40 billion yuan ($6 billion) project will take an estimated five years to complete. Chinese investors put up 70 percent of the funds for the project, with the rest coming from investors in Laos.

The rail line starts from the Mohan-Moten border area between the two countries, running over 414.33 kilometers, more than 62.7 percent of which will run over bridges and through tunnels. The construction of the bridges and tunnels is considered one of the decisive factors in whether the rail project will be built on schedule.

Language barriers, bad traffic conditions in the deep mountains and woods, and difficult living conditions were also obstacles that Zhou Xiaoxia, project manager of China Railway No 5 Engineering Group, faced when he started his work.

Facing these difficulties, Zhou and his team went deep into the woods to measure the route and prepare for the construction. "The China-Laos railway is one of the important routes that connects the two countries together," Zhou said. "It's a huge honor to be part of this project."

The rail line is designed for a speed of 160 kilometers per hour, using Chinese standards and equipment.

The project is not just a rail line, but represents the Lao people's faith in China, Zhou said. "The quality of the railway represents the image of China. We need to apply the same high standards as we use for the bullet train to the China-Laos railway," he said.

By the end of May, 40 percent of the phase one project had been completed with a zero defect rate. Zhou said he is confident he will finish his mission by the end of 2021.

"The company is leveraging its advantages in railway management, technology and resources to conduct research, as well as to offer construction and equipment manufacturing for the project," he said.