Houses flattened in Moore, Oklahoma (AP Photo KFOR-TV)
(NBC News) -- A huge tornado appeared to touch down just south of Oklahoma City on Monday afternoon, perhaps near a casino where people were sheltered, a helicopter pilot for NBC station KFOR reported.
A forecaster for the station said the tornado was kicking up a debris cloud about 2 miles wide as it tracked east into residential neighborhoods in the Moore area. It appeared as if the twister was dissipating and would miss the downtown area, The Weather Channel reported.
Parts of the Oklahoma City metropolitan area were under a tornado warning. The video showed what appeared to be a clearly defined tornado touching down outside the city.
Tens of millions of people in the Midwest are on edge as forecasters warn severe conditions could continue for the next couple days, NBC News' Jay Gray reports.
Tens of millions of people from Texas to the Great Lakes were warned to brace for severe weather one day after a tornado outbreak killed two elderly men in Oklahoma and turned a trailer park into splinters.
The gravest threat appeared to be in Oklahoma and parts of Missouri, but forecasters warned that strong storms, damaging wind and pounding hail were possible as far north as Minnesota and Wisconsin.
In all, an area covering 55 million people was under risk of severe weather, the National Weather Service said.
Severe thunderstorms, possibly accompanied by "a few tornadoes" were expected between 3 p.m. and 5 p.m. EDT in parts of Oklahoma.
"Initial storms are expected to produce very large hail and a few tornadoes," according to a NWS bulletin. "As storms grow in coverage ... damaging winds will become an increasing threat as well ... which could become widespread this evening."
On Sunday, twisters killed two men in Shawnee, Okla., ages 79 and 76, and injured 21 others. The state medical examiner confirmed the second death Monday morning.
The storms also destroyed mobile homes, flipped trucks and sent people across 100 miles running for cover. In Kansas, a weather forecaster was forced off the air as a tornado bore down on his station.
"You can see where there's absolutely nothing, then there are places where you have mobile home frames on top of each other, debris piled up," Mike Booth, the sheriff of Pottawatomie County, Okla., told The Associated Press. "It looks like there's been heavy equipment in there on a demolition tour."