Harbin authorities have said that overloading caused the collapse of a bridge that killed three and injured five on Aug 24.

Four trucks, with overloading of nearly 300 metric tons, were driving on the right side of a 122-meter-long ramp at the Qunli viaduct project.

The concentration of trucks made the ramp tilt to one side and crash to the ground, plunging all four vehicles to the pavement below, Liu Xingming, deputy head of the team investigating the accident, said at a news conference on Sept 19.

Liu, who is deputy director of Harbin administration of work safety, said the investigation found that the ramp's designer, contractor and supervisor all had top-rank qualifications, and no problems were found with the ramp's design and construction.

However, the official said, three trucks loaded with stones, which had set off from Jilin province, were found to be overloaded and were fined 450 yuan ($71) when they passed through a tollgate on the way to Harbin early on Aug 23.

Liu said road management authorities in Jilin's Dehui city, where the tollgate was located, should partly bear responsibility for the accident because they merely issued a fine for overloading and did not ask the trucks to unload goods.

Dereliction of duty by traffic police in Heilongjiang's Shuangcheng city and road management authorities in Harbin also indirectly caused the accident, he said.