Deaths from fentanyl overdoses have jumped by more than 2,100% in five years as the powerful drug has flooded the state.

But drug addiction experts say the haul may represent just a tiny fraction of the massive volume of the powerful synthetic drug that is flooding California, after being mostly an east coast phenomenon for years.

The number of deaths from fentanyl overdoses jumped by more than 2100% in California in five years, state figures show.

“Fentanyl has moved west,” said Dr Daniel Ciccarone, a professor specializing in addiction medicine at the University of California, San Francisco.

Instead, he said, it used to be distributed by drug trafficking networks supplying the east coast, who often slipped it into heroin supplies without telling users.

Another paper, co-authored by the Stanford University researcher Chelsea Shover, said the west coast may be three years behind on the same horrible trajectory of overdose deaths that overwhelmed the east coast several years ago.

The San Francisco police department’s drug bust operation in Oakland on 3 June, which resulted in five arrests, the seizure of seven kilos (16lb) of fentanyl, $45,000 in cash and two unregistered “ghost guns”, was only the latest in a recent string of major fentanyl seizures in northern California.

“We simply have not gotten to a proportional response to what amounts to an uncontrolled crisis,” he said, noting that though the nation has poured resources into combating the opioid crisis, deaths are still going up nationally, driven in part by the surge in west coast overdoses