The map of the to-be-built Ningbo-Zhoushan railway with an undersea tunnel shows the route between Ningbo and Zhoushan. [Photo/China Daily]

Preparatory work for the construction of the Ningbo-Zhoushan Railway－China's first high-speed railway with an undersea segment－connecting the Zhoushan Islands in East China's Zhejiang province with the mainland, has been completed, a senior official from Zhoushan said on Tuesday.

Construction of the railway, due to start by the end of this month, will involve a total investment of 27 billion yuan ($4.12 billion) and take six years to complete, Mao Jiangping, vice-mayor of Zhoushan, said at a news conference in Hangzhou, capital of Zhejiang.

Linking the Zhoushan Islands with the nation's high-speed railway network, the 76.4-kilometer line is set to notch up a number of world records.

The line's 16.18-km undersea tunnel from Ningbo to Jintang Island in Zhoushan will be the longest undersea high-speed rail tunnel in the world, while its 3.1-km Xihoumen Rail-Road bridge will be the longest in the world upon its completion.

With a designed train speed of 250 kilometers per hour, the new railway line will cut the travel time between Ningbo and Zhoushan to 26 minutes and between Hangzhou and Zhoushan to 77 minutes.

In another development, Mao said that construction of the 45.23-km Ningbo-Zhoushan Expressway is scheduled to start in 2022, which will have a maximum speed limit of 100 km/h.

"Ningbo and Zhoushan, located at the intersection of the Belt and Road Initiative's trade route and the Yangtze River Economic Belt, are important hubs and node cities in the Yangtze River Delta region," said Mao.

Upon completion, the railway and expressway will help Zhoushan better integrate into the Belt and Road Initiative and play a more important role in the integration of the Yangtze River Delta, he added.

It will also mean that all 11 cities in Zhejiang will be connected to the nation's high-speed rail network.

China aims to raise its global competitiveness in the railway sector by expanding its railway networks with wider coverage and higher speeds.

It plans to have 200,000 km of track laid by the end of 2035, including about 70,000 km of high-speed track, according to the latest national railway plan, issued in August by China State Railway Group, the country's top railway operator.

With the plan in place, all cities with populations of over 200,000 will be connected to the railway network by then, and those with a population of over 500,000 will be on high-speed rail lines, according to the plan.

Cai Jingwen in Hangzhou contributed to this story.