The storm known as a derecho that hit 13 mid-Atlantic and midwestern US states has caused fatalities, extensive property damage and widespread power outages.

More than a million people were still without power five days after the event, according to risk modeller Risk Management Solutions.

More than 40,000 insurance claims have been lodged so far, according to media reports.

Derechos are strong windstorms associated with a band of rapidly moving showers or thunderstorms that stretch along a straight path for hundreds of kilometres. The storms can travel as fast as 140kmh.

Standard US homeowners insurance policies cover windstorm damage, but there are restrictions on cover in some cases for residents near the Atlantic and Gulf coasts, according to the Insurance Information Institute.