Severe storms which have killed 42 people in the US and Mexico and flooded hundreds of homes could top more than $US1 billion ($1.3 billion) for motor vehicle insurance losses alone, according to the Insurance Council of Texas.

The auto insurance losses would come from severe flooding in Texas, according to council spokesman Mark Hanna. The floods hit Texas last week after days of rain due to huge storm systems which generated 19 tornadoes in Texas and Oklahoma.

Aon Benfield’s Impact Forecasting unit also says it expects financial losses from the severe weather and flooding to pass $US1 billion on an economic basis, but says it’s too early to make insurance industry loss assessments.

Late last Friday, President Barack Obama declared a major disaster for the state of Texas and ordered in federal aid. Texas Governor Greg Abbott has declared a state of disaster in 70 counties, which allows state resources to be used for storm response.

Farmers Insurance estimates insured losses at nearly $US105 million ($136.86 million), from more than 13,000 claims across Colorado, Iowa, Kansas, Nebraska, Oklahoma, South Dakota and Texas.

Catastrophe modeller AIR Worldwide says before the storms hit it was already the wettest May on record for many parts of the southern plains states, ending five years of drought in some areas.

The storm systems brought torrential downpours over two days.

More than 80,000 people lost power in Houston, Texas, and at Houston airport the single-day rainfall record – set in 1946 – was almost doubled on Monday as 11cm fell.

Flooding forced at least 2000 Texans from their homes, and hailstones bigger than cricket balls were reported in northeast Kansas.