The 36-kilometer bridge (22 miles), linking Shanghai with the busy port Ningbo in the Zhejiang Province, was open to traffic on Thursday and will reduce the trip between the two cities by 120 kilometers (75 miles).
Thousands of people gathered for the opening ceremony on Thursday, which was broadcast live across the country.
"The bridge has become famous and is expected to attract many visitors," the agency quoted Jin Jianming, deputy chief in charge of the construction project, as saying.
The cable-stayed structure, with a 32-km section spanning the Hangzhou Bay, was built at a cost of $ 1.69 billion partially funded by private investment.
About 2.5 million tons of concrete and 800,000 tons of steel were used to build the bridge. The work started in 2003 and was completed in June last year.
The bridge has six lanes and a maximum speed limit of 100 km per hour.
Heavy-goods trucks and vehicles transporting dangerous chemicals will be banned from using the bridge for a regulated period.