ABC NewsBy MAX GOLEMBO, EMILY SHAPIRO and MELISSA GRIFFIN, ABC News

(NEW YORK) — Tornadoes are tearing through Alabama Thursday afternoon and the threat is ongoing through the evening for “violent,” “long-track” twisters.

“Violent” means tornado winds could be 166 mph or greater, with ratings of EF-4 or EF-5. These tornadoes are often “long-track,” which means they may be on the ground for at least 25 miles.

In Shelby County, home to Birmingham, some homes have been completely destroyed, Sheriff John Samaniego said.

“Our priority at the moment is identifying those citizens in need of emergency medical attention,” the sheriff said. “We will then work with our partnering agencies to provide needed resources to our residents who are displaced. This search and outreach effort will continue throughout the night and into the early morning hours.”

Alabama and Mississippi are in the threat zone, as well as parts of Tennessee, Georgia, Kentucky, Indiana and Illinois.

A PDS (Particularly Dangerous Situation) tornado watch is in effect through at least 8 p.m. local time.

A tornado was confirmed at 12:30 p.m. local time near Moundville, Alabama, outside of Tuscaloosa — the same spot struck by a tornado eight days ago.

Just before 2 p.m. local time, an extremely large tornado was confirmed in Vandiver, Alabama, outside of Birmingham.

Alabama Gov. Kay Ivey has issued a state of emergency for 46 counties, and announced that the health department has rescheduled its Alabama National Guard vaccination clinic in Hale County due to the storm.

In Mississippi, more than two dozen people have taken shelter at an elementary school in Lowndes County ahead of the severe weather. Two other schools, each of which can hold about 400 people, also are open as shelters, the Lowndes County emergency management director told ABC News.

All shelters are providing hand sanitizer and masks, enforcing social distancing and checking people’s temperatures.

Multiple rounds of intense thunderstorms also are expected in the afternoon and evening across eastern Mississippi, northern Alabama and much of Tennessee, from Nashville to Knoxville.

Damaging winds are expected, especially in Tennessee and Kentucky. Wind gusts could reach 80 mph, and very large hail is possible.

By midnight, storms with damaging wind gusts will be moving through Atlanta and into parts of the mid-Atlantic and Ohio Valley.

The storms could also bring heavy downpours, so people should be mindful of possible flash flooding.

ABC News’ Elwyn Lopez contributed to this report.

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