The number of claims filed following the Oklahoma tornadoes now totals 32,433, for insured losses of nearly $US250 million ($263 million).

The second severe weather event to hit the state in a fortnight saw at least 76 tornado touchdowns, plus hail and flash flooding that also hit Kansas, Missouri, Michigan, Illinois, Indiana and Iowa.

At least 13 deaths have been reported, with hundreds injured.

The aggregate financial impact of light and moderate roof and tree damage over a large area will be considerable, according to reinsurance broker Guy Carpenter.

The severe weather was created by a combination of warm air, strong winds and low-pressure areas.

Oklahoma Insurance Commissioner John Doak has made a declaration allowing emergency claims adjusters to gain temporary licences to help consumers and expedite claims.

Meanwhile, AIR Worldwide has released a report on coastline risks.

The insured value of residential and commercial properties in US coastal counties now exceeds $US10 trillion ($10.5 trillion), the report says.

The sum has grown almost 4% a year in the past five years, compared with a compound annual rate of about 7% in the three years to 2008.

A slowdown in housing construction affected growth, but the number and value of exposed properties on the US Gulf and east coasts continues to increase, AIR Worldwide says.

The growth rate is expected to increase as the economy recovers.