Yazoo City, Mississippi (CNN) -- Massive cleanup efforts got under way Monday after several tornadoes ripped through the South, killing at least 12 people -- 10 in Mississippi -- and leaving a swath of devastation in the region, from Louisiana to Alabama.
A 3-month-old baby and two other children were among the fatalities. Dozens more were injured, and scores of homes leveled.
The tornado devastated neighborhoods from Mississippi's central western border with Louisiana northeastward to Alabama. It sheared roofs off houses, overturned cars, snapped hundreds of trees and plunged large parts of the state in darkness as it toppled power lines.
Five of the dead were from Choctaw County in north-central Mississippi; four were from Yazoo County, north of Jackson; and one was from Holmes County, also in north-central Mississippi, said spokesman Greg Flynn of the Mississippi Emergency Management Agency.
The storm roared on into Alabama, where authorities said it killed two people -- including a man whose car hit a tree in Etowah County, said Yasamie Richardson, a spokeswoman for the Alabama Emergency Management Agency.
In Walker County, a woman died after hitting her head while entering a storm shelter, Richardson said.
The National Weather Service on Monday gave the tornado that ravaged parts of Mississippi a preliminary rating of speeds of up to 170 mph. Yazoo was one of the hardest-hit counties.
Mississippi Gov. Haley Barbour said he will request emergency federal aid on Monday. Officials from the Federal Emergency Management Agency were scheduled to arrive Monday, anticipating an application for a disaster declaration, authorities said.
Barbour, who was in Yazoo City where his home is located, called the twister "gigantic" and said that in places it "seemed to be to be several miles wide."
The same storm system that unleashed Saturday's twister delivered severe weather to other parts of the South on Sunday, with tornadoes hitting Alabama and South Carolina.
The tornado traveled 150 miles across Mississippi, starting in the western part of the state and moving northeast before weakening as it moved into Alabama.
On Sunday, a tornado in Darlington County in northern South Carolina overturned at least four mobile homes, toppled trees and downed power lines.
Three people were hospitalized with minor injuries, according to Linwood Epps of the county's emergency management agency. He said that an elementary school was damaged, with part of its roof missing.
Alabama's emergency management officials confirmed a tornado touched down Sunday in Marshall County in the state's north.
At least one mobile home park and some homes in Albertville were destroyed, said CNN affiliate WAFF-TV in Huntsville, Alabama.
The tornado was part of a broad band of storms that stretched from Missouri to the Florida Panhandle.
Saturday's twister struck Louisiana before it moved into Mississippi. A Tallulah, Louisiana, police dispatcher said a chemical plant in the town had been damaged, but gave no further details.