Three people were killed and five injured when an eight-lane bridge in northeast China collapsed early on Friday, only nine months after it opened, state media said.

The bridge, part of an airport expressway in Harbin city, only opened last November after two years of construction that cost 1.9 billion yuan ($300 million), China News Service reported.

A 100-metre (320-foot) section broke off when four heavy trucks drove onto the bridge, plunging them to the ground, said a CCTV news reporter at the scene. The bridge was designed to handle up to 9,800 vehicles per hour.

Two people were killed on the spot, a third died later, and five remain in hospital.

"To break after apparently just under a year of operation, for sure there is a problem," said Huang Yi, spokesman for the State Work Safety Administration, which operates under the State Council, akin to a national cabinet.

The official Xinhua news agency said at least six major bridges have collapsed across the country since July last year, and that shoddy construction and over-loading were to blame.

China has rapidly expanded its road and rail infrastructure over the past decade as its economy has boomed, but critics say that safety has sometimes been overlooked in the rush to develop.

At least 40 people were killed when two high-speed trains collided near the eastern city of Wenzhou in July last year, and another train crash on Thursday in Heilongjiang province, where Harbin is located, left at least 24 people injured.

Authorities investigating Friday's incident will look into the bridge design and construction as well as the truck loads, the Harbin government said in a statement.

Thousands of people commented on the collapse on Sina Weibo, a popular Twitter-like service, with most blaming corruption.

"Just imagine, some corrupt official takes four-fifths of the project funds, that means the project manager can only make money by skimping on the job," said one user.

"I really want to yell at someone," said another. "Seeing the pictures is so tragic."