At least one tornado touched down in Southern Illinois on Sunday night, the authorities said, leaving one person dead, as residents in the area were inundated with National Weather Service warnings and advised to seek shelter.

At least one of the vortexes was considered “extremely dangerous,” according to the Weather Service. In Jefferson County, Ill., there were “multiple areas of destruction” from the tornado and one confirmed death, according to a statement from the sheriff’s office.

Videos posted to social media showed large masses of clouds and funnels and damage in the aftermath.

One post from Mount Vernon, Ill., in Jefferson County, showed snapped trees atop a vehicle and debris hanging from damaged branches.

Tiara Gabrielle Etheridge, who lives in Mount Vernon, said she took shelter when it was clear a tornado was approaching.

“My boyfriend was outside watching the clouds with our neighbor and once they started to circle we had to get our kids and run,” Ms. Etheridge said in a text message on Sunday. “Once we were a block or two away, we could see the entire funnel cloud forming DIRECTLY above our home.”

Ms. Etheridge said they found shelter and waited for the storm to pass before returning.

She added that she has lived there for several years and her home had never been seriously damaged.

“This is the first time we have felt in danger,” Ms. Etheridge said.

Storms that spawned the tornadoes were largely part of the same system, according to the Weather Prediction Center.

By Sunday night, there had already been at least 13 reports of tornadic activity or damage, said Scott Kleebauer, a meteorologist at the Prediction Center. Parts of southern and central Indiana were also under tornado warnings watches as the system churned eastward.

“That doesn’t mean that it’s 13 different tornadoes,” Mr. Kleebauer said. “Some of them are probably from the same tornado, but still, 13 is pretty significant across one small area of Illinois.”

Mr. Kleebauer added that he would not be surprised if, when official reports were completed, there were “at least three or four tornadoes out of this, and there could be more.”

Shortly after 6 p.m. Central, a tornado was confirmed in Marion County moving east at 35 miles an hour, according to the Marion County Emergency Management Agency.

There were no reports of injuries, according to the agency, but several outbuildings may have been damaged.

Just before 7 p.m. Central, the National Weather Service reported that “the tornado threat continues” across Southern Illinois.