TONGHAI, Yunnan -- Construction workers on Tuesday laid the last piece of a railway that will link southwest China's Yunnan province with the Association of Southeast Asian Nations (ASEAN) countries.

The Yuxi-Mengzi Railway has a total length of 141 km with a designed maximum speed of 120 km per hour. It passes through 35 tunnels and crosses 61 bridges, which together account for 54.95 percent of the line's total length.

The railway is part of the eastern line of the planned Pan-Asia Railway network, an international railway project that will also consist of central and western lines.

Funded by the Ministry of Railways and the Yunnan government, the railway has a total investment of 4.5 billion yuan (709.78 million U.S. dollars).

The railway is expected to become operational later this year and will boost land transportation between China and ASEAN countries.

The eastern route is designed to start in Kunming, capital of Yunnan, and pass through the cities of Yuxi, Mengzi and Hekou in Yunnan to connect with Vietnam, Laos, Thailand and Singapore.

Construction in Yunnan of the eastern line's last section, which will link Mengzi with the border city of Hekou, is going to plan, likely enabling the Sino-Vietnam railway to become operational first in the Pan-Asia Railway network, said a local railway official.

The new line will be a much more modern replacement to the 100-year-old line that links Kunming with Haiphone of Vietnam, the first transnational railway in southwest China, said Han Zhongping, deputy director of the Kunming railway bureau.

The 854-km Kunming-Haiphone line has a designed maximum speed of only 30 km per hour. It is the world's longest "narrow" line -- one meter wide, compared to the standard 1.435 meters wide.

Meanwhile, construction of several sections of the other two lines and also of lines linking major domestic cities like Shanghai is also under way.

Lu Dongfu, vice railway minister, said the huge investment on railway construction in Yunnan has major significance at a time when the country's railway investment is recovering.

The projects in Yunnan will become part of the national strategy to open up the southwest and spur economic growth in ethnic minority regions, according to Lu.

The robust construction is pushing the mountainous border province to the forefront of opening-up, said Liang Gongqing, head of the provincial railway construction inspection team. Railway investment over the past eight years totalled 53.7 billion yuan (8.5 billion U.S. dollars), he added.

The expanding network will bring Yunnan closer to other parts of China and also provide a more efficient and convenient passage for exchange and trade with southeast Asia, Han said.