Constructors work on a tunnel, part of the Beijing-Zhangjiakou high-speed railway in Beijing on Nov 2, 2017. [Photo/VCG]

The building of Qinghuayuan tunnel has begun Monday in Beijing as the Beijing-Zhangjiakou intercity high-speed railway construction enters its key phase, reported China News Service Tuesday.

The tunnel is located in Haidian district, extending underground from the Beijing North Railway Station for 6,020 meters before going aboveground to the north.

Chen Shuang, chief engineer of Beijing-Zhangjiakou railway project, said the Qinghuayuan tunnel will go through three subway lines, seven crucial city roads and 88 municipal pipelines.

"The tunnel is a shield tunnel with high risk as it is located in the city core and passes through some of the most complex underground layers and most important buildings," said Chen.

"Shield tunneling can minimize the destruction of current fundamental construction features such as roads, pipelines, pedestrian overpasses and bus stations, and also reduce noise pollution and the interference to people and residential communities," according to him.

The Beijing-Zhangjiakou high-speed railway has a total length of 174 kilometers with 10 stops, which is the first ballast track with maximum speed of 350 km/h, able to pass through Alpine regions and sandstorm areas, according to the Beijing Railway Administration.

The project is scheduled for completion by the end of 2019 and will shorten the trip between the two cities from the current three hours to just one hour.

It is a vital transportation construction for the 2022 Winter Olympic Games co-hosted by Beijing and Zhangjiakou.