State fire investigators have determined that transmission lines owned by Pacific Gas & Electric (PG&E) caused the deadliest and most destructive wildfire on record in California, officials said on Wednesday.

The wind-driven fire, dubbed the Camp Fire, erupted in the drought-parched Sierra foothills 280 kilometres north of San Francisco in November 2018 and raced with little warning through the town of Paradise, incinerating much of that community. It killed 85 people.

About 15,000 homes and another 4,000 structures were destroyed, and the death toll stands as the greatest loss of life from a single wildfire in California history. Several firefighters were injured.

Shares of San Francisco-based PG&E initially fell 3.1 per cent in after-hours trading following release of the California Department of Forestry and Fire Protection (Cal Fire) statement announcing the findings of its investigation. The stock later recovered and was trading at 0.2 per cent above the closing price of $18.10 US a share.

Cal Fire found last June that PG&E-owned power lines had sparked a separate series of wildfires that swept Northern California's wine country in 2017. But prosecutors from four affected counties later determined there was no basis to criminally charge the utility in connection with the so-called North Bay fires.

PG&E filed for bankruptcy in January 2019, citing potential civil liabilities in excess of $30 billion US from the North Bay and Camp Fires.