In this aerial photo taken on June 22, 2018, construction workers crane up a steel girder as they built a bridge across the Yuanjiang River along the China-Laos railway project in Yuxi, southwest China's Yunnan Province. Linking Yuxi in southwest China and the Lao capital Vientiane, the China-Laos railway is expected to be fully operational in December 2021. (Xinhua/Hu Chao)

Nearly 80 percent of the construction of the China-Laos railway has been completed, said Lao Deputy Prime Minister Sonexay Siphandone on Saturday.

The railway will serve as a key infrastructure for the economic corridor between the two countries and help boost trade, investment and tourism, said Sonexay at the China-ASEAN Expo held in Nanning, capital of south China's Guangxi Zhuang Autonomous Region.

With a designed speed of 160 km per hour, the China-Laos railway is expected to be fully operational in 2021.

Ground-breaking ceremony of the railway was held in December 2015, and the construction of the whole route officially started a year later.

China had invested a total of 12.5 billion US dollars in 782 projects in Laos by the end of June this year since 1988, making it the biggest investor in Laos, said Sonexay.

Chinese investments in Laos are mainly focused on infrastructure projects like hydropower plants, highways and power grids, according to the deputy prime minister.