Debris seen in the aftermath of a tornado in Franklin, Texas

Debris seen in the aftermath of a tornado in Franklin, Texas, in this image from social media.

Tornadoes killed at least three children in the South, authorities said on Sunday, as a massive storm system began drenching East Coast states.

A tornado touched down and spun toward Enigma, Ga., on Sunday, after 17 twisters were reported on Saturday and Sunday across the South from Texas to Alabama.

“We’ll be seeing severe weather from Florida to New York, with the most unstable parts so far in Georgia,” said meteorologist David Roth of the National Weather Service Weather Prediction Center.

More than 100 million people from the middle of the United States to the East Coast were at risk of extreme weather, facing warnings of heavy thunderstorms and another round of tornadoes, said NWS meteorologist Bob Oravec.

Nearly 6,000 U.S. flights were canceled or delayed, with most of the trouble at airports in Chicago, Dallas and Charlotte, N.C., according to FlightAware.com. Snow was falling in Chicago on Sunday, with 1 to 3 inches reported in central Illinois, as a result of the storm’s cold front.

Two children, siblings ages 3 and 8, were killed on Saturday when a tree fell on the car in which they were sitting in Pollok, Texas, said a spokesman for the Angelina County Sheriff’s Department.

A third child, Sebastian Omar Martinez, 13, drowned late on Saturday when he fell into a drainage ditch filled with flash floodwaters near Monroe, La., said Deputy Glenn Springfield of the Ouachita Parish Sheriff’s Office.

In another storm death nearby, an unidentified victim’s body was trapped in a vehicle submerged in floodwaters in Calhoun, La., Springfield said.

ABC News reported two more deaths after a tornado ripped through Hamilton, Miss. A spokesman for the Monroe County Sheriff’s Office said authorities were in Hamilton and could not be reached for confirmation.

Tornado warnings remained in effect on Sunday for southeastern Alabama’s Barbour and Russell counties, Oravec said.

“It’s still a pretty impactful day today. This morning, there is a lot of heavy rain moving through Alabama, into Georgia and eastern Tennessee. There are a few tornado warnings and heavy thunderstorm warnings,” Oravec said.

Soaking rains could snarl Monday morning’s commute on the East Coast before the storm moves off to sea.