LANZHOU, July 11 (Xinhua) -- A railway tunnel passing under a large area of red clay soil opened Wednesday, according to China Railway Tunnel Group.

Qingyang railway tunnel is a part of Yinxi rail line, linking Yinchuan, capital of northwest China's Ningxia Hui Autonomous Region and Xi'an, capital of Shaanxi Province.

About 90 percent of the 14-km tunnel passes under red clay soil. Construction of tunnels under red clay is very challenging due to its instability.

This is the first and longest railway tunnel built under red clay soil in China, said China Railway Tunnel Group.

Travel time between the two cities will be reduced from 14 hours to three hours. It is expected to become a major passage between China's western and eastern regions.