At least 4 people were killed -- including 2 children -- after powerful storms roared through the South on Saturday, spawning multiple tornadoes in several states as the threat for severe weather expands north on Sunday.

The Angelina County Sheriff's Office in Texas said an 8-year-old and a 3-year-old died when strong winds toppled a tree onto the back of their family's car in Lufkin, located about 115 miles northeast of Houston.

Capt. Alton Lenderman said the parents, who were in the front seats, were not injured.

In Mississippi, a man was killed in the town of Hamilton when a tree fell on his trailer.

Monroe County Road Manager Sonny Clay said at a news conference Sunday that 19 people were taken to hospitals for treatment, including two in critical condition. Hamilton, Miss., is located 140 miles southwest of Memphis, Tenn.

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The tornadoes were from a spring storm system that is shifting northward on Sunday, with the threat for severe weather focused on the Appalachians into the mid-Atlantic, according to Fox News Meteorologist Adam Klotz.

"We're talking about tens of millions of people with some stormy weather before this Sunday is over," he said Sunday on "FOX & friends."

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The National Weather Service's Weather Prediction Center said that a line of severe thunderstorms, ongoing from early Sunday morning, is expected to move into the Southeast through the remainder of the morning and early afternoon hours.

"Some fragmentation and possible weakening of this line is expected but a second round of storms is anticipated farther north into the Appalachians later this afternoon," the NWS

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In Central Texas, Robertson County Sheriff Gerald Yezak told the Associated Press a tornado hit the small city of Franklin on Saturday, overturning mobile homes and damaging other residences. Franklin is located about 125 miles south of Dallas.

The National Weather Service said preliminary information showed an EF-3 tornado touched down with winds of 140 mph. Crews will continue to survey the damage over the next few days.

Another possible tornado left damage in southeastern Alabama on Sunday morning.

Power poles and trees were knocked over and parts of buildings were left hanging across utility lines in Troy, located about 50 miles south of Montgomery. A mobile home community was damaged, but no injuries are being reported.

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The National Weather Service detected a possible twister on radar, but it's unclear whether a tornado or straight-line winds caused the damage. More than 140,000 customers remained without power in Texas, Mississippi, Louisiana, and Arkansas as of Sunday morning.