Beijing  - China on Thursday opened what it touted as the world's longest sea bridge, establishing a new link to bustling Shanghai.

The 36-kilometre-long structure spans Hangzhou Bay and connects Shanghai with Ningbo.

The 11.8-billion-yuan (1.7-billion-dollar) bridge cuts the driving distance between the two key cities of the Yangtze River Delta by 120 kilometres, the official news agency Xinhua said.

After a four-and-a-half-year construction, the six-lane bridge was inaugurated Thursday and was to open on a trial basis at midnight, Xinhua said.

It surpassed another Shanghai structure for the title of the longest sea bridge, beating out the 32.5-kilometre Donghai Bridge, which links China's largest city to the Yangshan deep-water port.

It also ranks among the longest bridges overall in the world, falling just short of what is considered the longest, the 38.4-kilometre Lake Pontchartrain Causeway Bridge in the southern US state of Louisiana.

Thirty per cent of the financing for the Hangzhou Bay project came from private investors, a first for such a large Chinese infrastructure project, Xinhua said. (dpa)