An official inquiry blames China's state-owned oil giant Sinopec and local authorities in the city of Qingdao for a November pipeline explosion that killed 62 people, state media reported Thursday.

The State Administration of Work Safety (SAWS) found that Sinopec and the Qingdao city government "are responsible for not identifying and correcting potential safety hazards", state broadcaster China Central Television reported, citing a summary of an investigation.

The probe found that the pipeline itself was improperly designed and the emergency response in the wake of the explosion -- which also injured 136 -- was poorly handled, it said.

SAWS spokesman Huang Yi said Thursday that the incident was caused by corrosion of the pipeline, which burst and leaked into the city's sewage network, the official Xinhua news agency reported.

The blast itself was triggered by sparks from a hydraulic hammer that was not explosion-proof.

Sparks were created when it was used on a sewer cover plate hours after the pipe burst, Huang said, according to Xinhua.

"The report has been handed over to the State Council and will be released to the public later," the CCTV summary said. The State Council is China's cabinet.

Xinhua called the November 22 explosion China's deadliest since at least 2005.

Pictures show it ripped roads apart, turned cars over and sent thick black smoke billowing over the city.

The blast occurred seven hours after an oil leak was first spotted, and questions remain as to why local residents were not ordered to evacuate in the intervening period.

Seven Sinopec employees and two Qingdao city workers have been detained in connection with the explosion.

Sinopec issued an apology for the incident but denied that it was slow to respond, maintaining that it contacted local police and firefighters as soon as the leak was found.

According to the Xinhua report, Huang also faulted the "disorderly municipal design" at the site, noting that the pipeline had been installed too close to city buildings and was intertwined with the local sewage system.