XINING - The world's highest tunnel for high-speed trains in Northwest China was completely linked up on Thursday, paving the way for the operation of the line linking Gansu province and Xinjiang Uygur autonomous region.

With altitudes of up to 3,607.4 meters, the 16.3-km-long tunnel passes through the Qilian Mountains with two sections and a bridge. It began construction in 2009.

The tunnel's complete joining means the most difficult part for the Lanxin high-speed railway has been solved, said Guo Yuhong, an official in charge of the tunnel project from China Railway 20th Group Co Ltd.

The 1,776-km Lanxin high-speed railway links Lanzhou, capital of Gansu, with Urumqi, capital of Xinjiang. It runs across Gansu and Qinghai provinces to Xinjiang, traversing the wind ravaged Gobi Desert.

The line is planned to be put into use at the end of this year. It is designed for trains running at more than 200 km per hour. It will cut the train travel time between Lanzhou and Urumqi to eight hours from about 20 hours.