China says the first five trains linking Tibet to the rest of China are set to depart from the mainland on July first.
The official Xinhua news agency said Saturday that tickets for all five trains are already sold out.
The first trains will depart from the Chinese cities of Beijing, Chengdu, Xining, Shanghai and Guangzhou.
China's railway into Tibet, which is not yet fully operational, is the world's highest. Eighty percent of the line is above four thousand meters in altitude, and it rises above five thousand meters in some places. Passenger coaches must be pressurized in the same way as aircraft cabins.
Critics say the railway will harm Tibet's environment by opening its timber and mineral resources to further exploitation.
Chinese officials say the railway will open new markets for Tibetan products and boost its tourism industry.