Cars roll over after oil pipeline blast in Qingdao, East China's Shandong province, Nov 22, 2013. [Photo/Asianewsphoto]

QINGDAO - The deadly oil pipeline blasts in East China's Shandong province on Friday exposed three severe problems of human errors, and the accident was a "very serious dereliction of duty", a senior official in charge of the country's work safety said Monday.

The problems include the unreasonable layout of oil pipelines and urban drainage pipes, negligence of duty on pipeline supervision, and unprofessional handling of oil leakage before the blasts, said Yang Dongliang, director of the State Administration of Work Safety.

Yang made the remarks in Qingdao city at a meeting of an investigation team for the accident, which has left 55 people dead, nine missing and 136 hospitalized as of Monday morning.