LANZHOU - Lanzhou, capital of Northwest China's Gansu province, will kick off construction on a subway network next month, the city's mayor said Wednesday.

The remote city, which sits on the upper reaches of the Yellow River and is sandwiched by craggy mountains to the east and west, will be the second Northwest China city to have a subway system after Xi'an, Mayor Yuan Zhanting said at a press conference.

"Lanzhou's urban railway construction plan has been approved by the National Development and Reform Commission, and construction will begin in early July," he said.

The planned urban railway network will consist of six subway lines running 207 km, Yuan said.

Three of the subway lines, coded Line 1, Line 2 and Line 3, will extend 90 km in the city proper, while the three outer lines, coded Line 4, Line 5 and Line 6, will run 117 km, connecting the city center with Lanzhou Zhongchuan Airport, Yuzhong county and Gaolan county, respectively.

The first two lines will cost about 23 billion yuan ($3.6 billion) and be completed by 2020, said Yuan.

The fast-growing population and ever-increasing amount of motor vehicles have made building subways in Lanzhou essential, he said.

The city has a population of 3.6 million.