Severe storms and tornadoes have killed at least 12 people and damaged or destroyed more than 900 properties in the southern US states of Mississippi and Alabama.

Mississippi suffered the brunt of the bad weather, including winds of up to 260kmh, global reinsurance broker Guy Carpenter said.

A preliminary damage report released by the Mississippi Emergency Management Agency on Thursday reported that 10 people were killed and 731 homes damaged statewide.

Mississippi Governor Haley Barbour has declared a state of emergency in 17 counties and has applied for federal disaster assistance for affected areas.