At least 21 people have now been confirmed killed as tornadoes ripped through the central United States over the weekend Monday while severe storms threatened to roil parts of the East Coast.

The system, which struck the Southern Plains region beginning late Saturday, overturned vehicles and ripped up homes, leaving a wake of deadly destruction in its path.

Storms were still likely to produce damaging wind and hail as they pushed eastward Monday, part of the U.S. Memorial Day holiday weekend, as well as possibly produce "isolated tornadoes" in the eastern Mid-Atlantic, the National Weather Service said.

Over the weekend eight people died across northwest Arkansas in the severe weather, Lacey Kanipe, a public information officer with the state's Division of Emergency Management, told AFP.

In Kentucky four people died as tornadoes ripped through the state, Gov. Andy Beshear said during a news conference Monday, explaining that "at least a few" twisters touched down in the state, including one that traveled on the ground for some 65 kilometers (40 miles).

The storms also caused "significant damage to the power infrastructure," said Beshear, who declared a state of emergency, adding that it could be days until all power is restored.

Seven people died in Texas after a tornado ripped through the Valley View area north of Dallas, Cooke County Sheriff Ray Sappington told reporters.

The twister destroyed homes and a gas station, and overturned vehicles on an interstate highway. Sappington called the damage "pretty extensive," in an interview with The Weather Channel.

And in Oklahoma, at least two people were dead after a tornado hit Mayes County late Saturday, the county head of emergency management, Johnny Janzen, told the Fox News affiliate in Tulsa.

Storm chasers shared impressive footage of tornadoes ripping up roofs and tearing through trees, causing power lines to spark and sending branches and debris flying.

As far north as Indiana, the start of the Indianapolis 500 motor race was delayed for four hours Sunday due to storms in the area, with fans asked to exit the stands and seek shelter.

More than 530,000 customers were without power midday Monday in states stretching from Arkansas up to West Virginia and south to Georgia, according to the website Poweroutage.us.

Tornadoes are relatively common in the United States, especially in the center and south of the country.