The “bomb cyclone” that hit the US Midwest last week is the northern winter’s biggest insurance event, the Insurance Information Institute says.

States of emergency were declared in states including Iowa, Nebraska, Wisconsin and South Dakota as the “bombogenesis” – an extraordinary combination of wind-driven snow and severe rainfall – rolled in.

The storm caused flooding along the Mississippi and Missouri rivers and strong winds and heavy snowfall across many Midwest states. At least two deaths have been reported, and thousands in affected towns were evacuated as floodwater surged.

“This phenomenon is a rare one for the landlocked region and has the potential to break all-time, low-pressure records for parts of Colorado and Kansas,” the National Oceanic and Atmospheric Administration said.

Winter storms usually cause more than $US1 billion ($1.41 billion) a year in insured losses in the US.