California's state fire protection agency Cal Fire has confirmed that electrical power lines sparked the deadliest and most destructive fire in the US state's history.

The so-called Camp Fire in northern California left 85 people dead in November, burned through more than 60,000 hectares of land and destroyed nearly 19,000 houses and other structures.

The flames consumed the small town of Paradise

Pacific Gas and Electric (PG&E) had acknowledged that its equipment was probably to blame for the disaster.

Cal Fire has made it official, after concluding what it called "a very meticulous and thorough investigation."

Very dry vegetation, strong winds, high temperatures and low humidity fuelled the fire and caused "extreme rates of spread," the agency said.

A second ignition point that was eventually consumed by the first fire was also caused by PG&E power lines, Cal Fire said.

A fallen power line is seen on top of burnt out vehicles on the side of the road in Paradise

Cal Fire's full report was not released to the public but rather passed on to prosecutors in Butte County, who will decide whether to start legal proceedings over the fire.

The report could lead to charges being filed against PG&E, which has already been sued by many people who lost their homes and businesses and by insurance companies and local civic associations.

They accuse the utility of chronic negligence in the management of its facilities.

The company is looking at billions of dollars in liability if courts side with plaintiffs.

In January, PG&E filed for protection from creditors under US bankruptcy law.