Chinese police have arrested nine people in connection with last week's oil pipeline explosion in the eastern port city of Qingdao that left 55 people dead and more than 140 others injured.

Seven of the suspects are with oil giant Sinopec, the proprietary company of the pipeline, while the other two are associated with the Qingdao economic development zone, the South China Morning Post said Tuesday.

A preliminary investigation attributed the explosion to "human error" and cited as possible causes "bad urban planning, poor pipeline maintenance and an inadequate response."

What is not known, however, is the degree of responsibility for the disaster that will be assigned to the local government and the state oil company.

The explosion, which destroyed a highway running alongside the pipeline and blasted down buildings, was apparently caused by oil leaking into the sewer system.

Some media outlets and Qingdao residents have slammed the fact that no alert was issued before the pipeline blew up, because the explosion occurred while workers were repairing a leak that had been detected seven hours previously.

The Qingdao government, for its part, said that it had not been notified about the oil leak until the explosions occurred, though Sinopec says it had warned district authorities beforehand, the Morning Post said. EFE