TULSA, Okla. — Forecasters warned of possible tornadoes as thunderstorms rolled across parts of the South on Thursday, a day after at least seven people were injured when severe storms spawned multiple tornado touchdowns in northeastern Oklahoma.

Hail and damaging winds were moving across the lower Mississippi River Valley, and the National Weather Service said the heavy rain may produce flash flooding in some areas. The weather service’s Storm Prediction Center said the greatest threat of tornadoes and large hail was in northern Mississippi and Alabama, along with parts of Tennessee and southern Kentucky.

Forecasters say more than 8 million people will be at an “enhanced” risk of severe weather in parts of Mississippi, Alabama and Tennessee.

In Oklahoma, a tornado touched down and lifted up numerous times Wednesday night as it swept through the northern Tulsa and Owasso areas, according to weather service meteorologist Amy Jankowski.

About a square mile of a mostly residential area sustained damage, with one home destroyed and other residences and businesses sustaining roof and structural damage, Tulsa Fire Department spokesman Stan May said.

Police and fire officials were going door to door in the area. There were no immediate reports of anyone missing, May said.

“We want to check each house,” he said. “We’ve got some elderly people in the area. We want to make sure people have the medicines they need.”

Seven people were transported to hospitals by Emergency Medical Services Authority, an ambulance service provider, spokeswoman Kelli Bruer said. Bruer said one was in critical condition and several were in serious condition. May said a few other people suffered minor injuries but declined treatment.

Tulsa streets and water departments were assisting with road barricades and debris removal.

In Louisiana, the National Weather Service issued a flash-flood watch for northern parts of the state until 7 p.m. Thursday. Forecasters predicted that multiple rounds of strong thunderstorms would produce 2 to 4 inches of rain, and perhaps 6 inches in some parts of the state.

“Heavy rain from waves of storms could renew flooding over north Louisiana,” said Cynthia Palmer, a forecaster at the weather service’s office in Shreveport, Louisiana.

The ground remains saturated in that part of the state, which saw record flooding earlier this month, Palmer said.

In northern Mississippi, forecasters said thunderstorms would bring rainfall amounts of 2 to 4 inches. A flash-flood watch was in effect through Thursday evening.