Rising insurance losses in the US could reach up to $US5.5 billion ($5.14 billion) following severe tornadoes that lashed southern parts of the country last month, according to risk modeller AIR Worldwide.

Initial assessments show that more than 8000 buildings and homes were caught in the path of the outbreak of category four and five tornadoes, which swept across several states from April 22 to April 28.

In Mississippi the number of homes destroyed has reached 2527. Virginia lost 443 homes while Georgia has about 75 to 100 homes that have either been damaged or destroyed.

But AIR Worldwide says Alabama has been the hardest hit, with more than 5000 properties destroyed in Tuscaloosa alone and 38 of its 68 counties declared disaster zones.  

The modellers say engineers are particularly interested in the performance of commercial structures in Tuscaloosa that were in the centre of a tornado’s track.

Scientist Tim Doggett says large commercial structures in the city were reduced to rubble.