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Media captionProperties in Franklin, Texas, were flattened by the tornado
At least eight people have died and dozens were injured after storms triggered tornadoes and flooding across several southern US states.
In Texas, two children died after a tree fell on their family car. The parents, who were in the front seats, were not injured.
Deaths were reported across Mississippi, Texas and Louisiana.
Some of the injured could not be rescued for hours due to debris on roadways, according to US media.
Authorities say at least 11 tornadoes touched down in three states before the storm began moving towards the East Coast.
Tornado warnings have been issued for Monday in Ohio, South Carolina and Virginia.
In Pollok, Texas – about 150 miles (240km) southeast from Dallas – two children were killed when their family car was hit by a falling pine tree.
According to Capt Alton Lenderman of the Angelina County Sheriff’s Office, the tree “flattened the car like a pancake”, but the parents, who were riding in the front of the vehicle, were not injured.
The children were aged eight and three.
In Alto, Texas, one person was killed and around two dozen others were injured after a suspected tornado struck a Native American cultural event, Cherokee County officials told the Associated Press.
Franklin, Texas was heavily damaged with nearly 60 buildings destroyed, local authorities say, including around 55 homes and several public buildings.
Hamilton, Mississippi, also saw dozens of homes destroyed, along with the community’s fire station.
“We took a direct hit,” one firefighter said over the radio, according to CNN. “The fire station (is) gone.”
In Monroe County, Mississippi, a 95-year-old man identified as Roy Ratliff, died after a tree fell on his mobile home.
Flash flooding in Bawcomville, Louisiana led to the death of a 13-year-old boy, who was found drowned in a drainage canal.
Near Birmingham, Alabama, a worker was killed after being struck my a vehicle while helping clear trees from a roadway.
On Monday, the storm system moved east, causing travel delays in New York, New Jersey and Pennsylvania.
Windy conditions and rain have been forecast for the Boston Marathon as well.