Dozens of people are feared dead after severe weather swept America’s southern states.

Many residents spent part of the night early on Monday (local time) sheltering in basements, closets and bathroom tubs as sirens wailed to warn of possible tornadoes.

The initial death toll was put at 12 when authorities first assessed the damage but by Tuesday morning (Australian time) the US media was reporting the number was steadily rising.

USA Today reported that 11 people had been killed in Mississippi, nine were found dead in South Carolina, and six more died in northwest Georgia. Others had been killed by falling trees or became trapped inside collapsed buildings, in Arkansas and North Carolina.

The Chattanooga, Tennessee area and several counties in northwest Georgia appeared to be particularly hard-hit.

Murray County, Georgia, fire chief Dewayne Bain told WAGA-TV that two mobile home parks were severely damaged, with five people killed and five others hospitalised after a narrow line of storms left an eight kilometre-long path of destruction.

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Another person was killed when a tree fell on a home in Cartersville, Georgia, the station reported.

At least 14 people were hospitalised in the Chattanooga area, where search-and-rescue teams from at least 10 fire departments were going door to door responding to more than 300 emergency calls for help, the fire department said.

The storms blew onward through the night, causing flooding and mudslides in mountainous areas, and knocking out power for about 750,000 people in a 10-state swath ranging from Texas to Georgia up to West Virginia, according to poweroutages.us.

The National Weather Service tallied hundreds of reports of trees down across the region, including many that punctured roofs and downed power lines.

NEW TORNADO WARNING: Parts of Berkeley County you are now under a Tornado Warning until 8 AM! The storm is moving East at 50 mph! If there is a tornado, it is likely wrapped in rain and you will be unable to see it! Please do not try to look outside. TAKE COVER IMMEDIATLY! pic.twitter.com/ES4HtgDVMc

— Bill Walsh (@BILLWALSHTV) April 13, 2020

Several apparent tornadoes spun up in South Carolina, where dozens of homes appeared damaged in a line from Seneca to Clemson. Emergency officials were working to open shelters in the North Carolina mountains, where up to 13 centimetres of rain fell in a few hours.

Mississippi Governor Tate Reeves declared a state of emergency on Sunday night after he said several tornadoes had struck the state.

The National Weather Service advised that the storm front would blow into the mid-Atlantic states on Monday, bringing potential tornadoes, wind and hail.

Another day of hazardous weather is forecast for parts of the eastern and southern U.S. with heavy rainfall, gusty winds, the risk of flooding, and severe thunderstorms. Check https://t.co/7995b2OMng often for updates. pic.twitter.com/pnwXW1wRjd

— National Weather Service (@NWS) April 13, 2020

News outlets reported downed trees, flooded streets and other damage in Alabama, Tennessee and Georgia, but the National Weather Service hadn’t immediately confirmed additional tornado touchdowns.

There were no immediate reports of serious injuries in Louisiana, even though the storm damaged between 200 and 300 homes in and around the city of Monroe, Mayor Jamie Mayo, told KNOE-TV.

The National Oceanic and Atmospheric Administration on Sunday called the tornado “an exceptionally rare event”.

In the late afternoon the NOAA warned on its website of possible wind speeds of up to 330kph and two large supercell thunderstorms that could strike some areas twice.

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The tornado is still on the move through the states of Alabama and Georgia.

Before the storms moved into Mississippi, the weather service reported multiple tornadoes and damaging winds over much of northern Louisiana. There were no immediate reports of serious injuries.

Utility companies reported thousands of power outages.

-AAP