Economic losses from the San Francisco Bay area earthquake last month are likely to top $US2 billion ($2.1 billion), Impact Forecasting says.

But insured losses from the region’s largest quake in 25 years may be limited to hundreds of millions of dollars, because the area’s earthquake insurance penetration rate has dropped to only 5.3%.

“The August 24 Napa County event serves as a reminder of the unpredictability and costly impacts of the peril,” Impact Forecasting Associate Director Steve Bowen said.

Quake insurance penetration rates across California have fallen to about 10% overall from 33% in 1996, according to the Aon Benfield catastrophe modelling subsidiary.

Elsewhere last month, a magnitude-6.1 quake in China’s Yunnan province killed at least 617 people and caused economic losses of at least $US6.3 billion ($6.7 billion), while quakes also hit Peru, Ecuador, Iran, Algeria and South Africa.

“Despite the upcoming historical peaks of the Atlantic and Pacific tropical cyclone seasons, earthquakes were the primary focus during August,” Mr Bowen said.

Flooding in the US midwest, northeast and mid-Atlantic regions caused economic losses of more than $US2 billion ($2.1 billion), with losses to private insurers and the National Flood Insurance Program exceeding $US500 million ($533 million).

Rain, flooding and weather events caused damage in China, India, Nepal, Japan, Bangladesh, Cambodia, Pakistan and South Korea. There were no significant natural disasters in Australia and New Zealand last month.