Insured losses from the tornados which devastated property across six southern US states will be between $US2 billion ($1.86 billion) and $US5 billion ($4.65 billion), according to risk modeller Eqecat.

But Alabama Insurance Commissioner Jim Ridling says losses from Alabama alone are expected to exceed $US2 billion.

Hurricane Katrina caused $US1 billion ($930 million) in insured losses to Alabama, while Hurricane Ivan amounted to $US2 billion in losses in the state.

Alabama, along with Mississippi, Tennessee, Georgia, Virginia, Arkansas and Kentucky, was hit by the second-deadliest tornado outbreak on record, with more than 350 reported tornado landfalls at the end of April.

More than 330 people were killed, with at least 230 fatalities in Alabama.

“In all my years in the insurance industry I have never seen anything so violent and widespread,” Mr Ridling said.

Eqecat says close to 10,000 buildings have been destroyed.