Two sections of the railway connecting Sichuan province and the Tibet autonomous region are expected to start construction before June, a political adviser said on Sunday.

Lu Chunfang, an academician of the Chinese Academy of Engineering, said sections will link Ya'an and Xinduqiao in Sichuan province and Bomi and Nyingchi in Tibet and are inviting public bidding right now.

Lu described the Sichuan-Tibet railway as the most challenging railway construction project in human history.

"Although China has abundant experiences in constructing all types of railways, including high-speed and railways at high altitude and carrying heavy hauls, it is insufficient to only rely on previous experiences to build the Sichuan-Tibet railway," he said, adding that innovations are the key to solving difficulties.

Lu, a member of the Chinese People's Political Consultative Conference National Committee, made the remarks via a video interview on the sidelines of the ongoing fourth session of the 13th CPPCC National Committee.

As the general director of the Qinghai-Tibet railway, the first railway to Tibet, he said the new line is more difficult because of more complicated geological conditions, posing extreme difficulties upon construction.

The 1,838-km Sichuan-Tibet railway has three parts. The Chengdu-Ya'an section opened in December 2018. The Lhasa-Nyingchi section started construction in 2015 and is still underway. The middle section between Ya'an in Sichuan and Nyingchi in Tibet is the most difficult part and started construction in November, last year.

The two sections, which are expected to start construction before June, belong to the middle section of the line.