Construction of a high-speed railway bridge set to shorten the travel time between Shanghai and Zhejiang's coastal city Ningbo started recently, authorities said.

The 25-kilometer Hangzhou Bay Cross-Sea Railway Bridge is an important section of the high-speed railway connecting Jiaxing and Ningbo in Zhejiang province, an integral part of the one-hour traffic network in the Yangtze River Delta region.

Upon its scheduled completion in five years, the new section of railway with a speed of 350 kilometers per hour, will reduce travel time from Shanghai to Ningbo from two hours to one hour. It will also shorten the traveling hours from Beijing to Ningbo by 90 minutes to five hours.

There is a traditional connection between Shanghai and Ningbo. Both are port cities that have been open to international trade for more than a century and many Shanghai families are originally from Ningbo.

Despite the close kinship, travel between the cities has long been impeded by Hangzhou Bay. It used to take at least three to four hours to travel between the cities as people had to detour to Hangzhou.

It was not until 2008 when the Hangzhou Bay Bridge, which connects Jiaxing and Ningbo, was opened, that travel time between the cities was reduced to two hours by car.

However, experts consider it not efficient enough for the further integration of the Yangtze River Delta region, which aims to become the world's sixth largest urban agglomeration.

The region, which consists of Shanghai and cities in Jiangsu, Zhejiang, and Anhui provinces and with a population of 220 million, accounts for one-sixth of China's total population and a quarter of the country's economy in 2017.

Lu Dadao, an academician of Chinese Academy of Sciences, said the first step for further regional integration is to build a one-hour traffic network centering on Shanghai.

"The ideal one-hour traffic network shall include cities such as Suzhou, Wuxi, Changzhou of Jiangsu provinces as well as Jiaxing and Ningbo, covering a total area of more than 20,000 square kilometers," Lu said.

A high-speed railway connecting Shanghai and Ningbo has been put forward for the vision with the construction of a cross-sea bridge being a major challenge.

"The cross-sea railway bridge would provide the opportunity for Pudong New Area to become a comprehensive transportation hub complete with a harbor, airport and high-speed railways serving the region so as to accelerate the resource flow of Hangzhou Bay," Wang Guoping, deputy director of the Consulting Committee of Zhejiang Provincial People's Government, was quoted as saying by the Shanghai Observer.