The latest run of US tornados could cost insurers between $US1 billion ($943 million) and $US3 billion ($2.83 billion), according to modelling firm Eqecat.

The latest tornado was centred on Joplin, Missouri, and is the deadliest since 1947, with reports of more than 100 people killed.

Eqecat previously estimated insured losses of $US2 billion ($1.89 billion) to $US5 billion ($4.7 billion) for tornados which struck around Alabama in late April, making this tornado season the costliest on record.

Up to a quarter of the 2000 buildings in Joplin have been completely destroyed, according to city officials. Another 5000-10,000 buildings are listed as having sustained damage.

It’s believed US primary insurers will carry the majority of the losses within their reinsurance retentions, but the tornados may trigger some catastrophe aggregate programs and excess of loss cat programs.

The mounting tornado losses come just prior to the commencement of the US hurricane season, due to officially begin on June 1.