A major earthquake in California’s Napa Valley wine country could cost insurers up to $1.5 billion in claims.

The 6.0 magnitude quake, the biggest to hit the US state’s Bay area in 25 years, hit on Sunday morning, injuring more than 200 people and damaging buildings and wineries in the Napa Valley, which lies northeast of San Francisco.

At least 49 buildings in the town of Napa have been listed as unsafe to enter, while some wineries suffered damage to bottle and barrel storage areas and production equipment.

And private homes in the region have also suffered significant damage as a result of the earthquake.

Dr Patricia Grossi, an earthquake expert and senior director of model product management at analysts RMS, said: “There is evidence of serious damage to older, residential wood frame structures and a large number of chimneys toppled as a result of the earthquake.”

RMS also reported “extensive damage” to unreinforced masonry buildings and facades, particularly plate glass, among buildings in downtown Napa, as well as broken water mains and fires.

Among the firms exposed to claims are Zurich, American International Group and Ace’s INA Group, all of whom have a presence in Bermuda.

Claims have already been made to insurance firms — but analysts warned that it will be some time before a full picture of the damage involved can be painted.

Chuck Watson, of risk modelling and assessment firm Kinetic Analysis Corp, said: “Weaker events, or the fringe of stronger events, people at first glance look around and go ‘oh, great, the building didn’t fall down.’ But then you start getting in there and doing inspections.”

But losses to insurance companies are likely to be limited by earthquake deductibles — which tend to be high — and a low rate of take-up for earthquake insurance in California.

It is estimated only about six percent of homes in the Napa Valley area are covered by earthquake insurance, according to the New York-based Insurance Information Institute.

But experts said that major earthquakes lead to a spike in people buying earthquake insurance.