Engineers completed the major section of a railway bridge on Tuesday on the Wujiang River, considered the most difficult and complicated project of a 625-kilometer-long railway linking Southwestern China and Central China.

Staff members from the China Railway Engineering Corp (CREC) finished the main span of the Wujiang Right-Line Bridge, which is 460.1 meters long with four piers, on the river, a "natural barrier" that flows through rolling hills in Fuling district of Chongqing and empties into the Yangtze River in the north.

The Yangtze is the longest river in Asia while the 1,037-kilometer-long Wujiang is the largest river in Southwest China's Guizhou province.

The enormous metal and concrete bridge is part of the Line 2 Railway of the existing artery linking southwestern Chongqing and Huaihua in Central China's Hunan province, and the line is considered a key project in the national railway network, according to Wang Wei, Party secretary of the working team from the No 2 Branch Company of CREC No 4 Group Co Ltd - the company building it.

Upon completion by 2020, the single-track Line 2 will run side by side along the Chongqing-Huaihua Railway to boost trans-regional transport, with the section between Fuling and Huaihua having a length of 499 kilometers.

According to Wang, construction of the railway bridge started in October 2016 and it is part of the 10.5-kilometer-long project they built with an investment of 327 million yuan ($47 million).

The railway bridge, which has to span the Wujiang River and the G319 national highway, is really a hard nut to crack, as the foundations of the tallest No 3 pier stand 137.19 meters high and the pier's weight reaches some 1,400 metric tons, he said.

As most of the hard work is on the Wujiang River, the technicians have created 16 patents, which they have applied to the State patent regulator granting five of them so far to the No 2 Branch Company of CREC4.

According to Zhang Haolong, manager of the working team from the CREC4 No 2 Branch Company, building Line 2 of the existing Chongqing-Huaihua Railway is of vital importance to the southwestern, central and southern regions.

Chongqing, located in southwestern China, is the fourth municipality under the direct leadership of the central government after Beijing, Shanghai and Tianjin, while Fuling district, with a known history of more than 2,000 years, was renowned as the ancient capital of the Ba State.

Fuling, where the Yangtze and the Wujiang rivers converge and whose mountain ranges present a spectacular appearance, boasts exquisite scenery, rich cultural and modern industry, Zhang said, adding that the district's shale gas capacity has reached a record amount of 10 billion cubic meters.

Fuling is also known as the "hometown of Zhacai (or Cha Tsai)", a type of pickled mustard plant stem originating from Chongqing and serves as a commodity distributing center for the 20-odd counties and cities in the Wujiang River Valley, noted Gao Lian, deputy publicity chief of the No 2 Branch Company of CREC4.

While its traditional manufacturing industry is making great advances, Fuling's six expanding industries are also gaining ground, Gao said.

The district is also known for its 816 Underground Nuclear Project - the largest man-made cave complex as an industrial base for nuclear raw materials, which was suspended in 1984 due to the adjustment of national strategy, he said.