CHICAGO (AFP) - Oklahoma was hit late on Friday by potentially deadly tornadoes not far from the battered town of Moore, where a powerful twister struck less than two weeks ago, killing 24 people.
Weather forecasters declared an emergency for parts of the tornado-prone midwestern state, amid reports that several twisters had struck the area around Oklahoma City.
One large tornado touched down west of Oklahoma City, the state's biggest city, news reports said, but no injuries were immediately reported.
Oklahoma Governor Mary Fallin said late on Friday that she was "heartsick" that Moore, struck by a powerful tornado on May 20, could be hit once again.
"I'm very concerned right now," Ms Fallin told CNN.
"I'm here across from the capitol and it is hailing and blowing and raining extremely hard. Our tornado sirens have gone off several times," she said.
Ms Fallin said she was particularly worried about high traffic on the midwestern state's major highways, which could be in the direct line of the tornado.
"We hope this storm passes through and it's just some rain and hail. But we do know the winds are whipped up pretty good and it's just a loud rumble outside. It was hailing just loud from all the thunder and lightning," she told CNN.
News reports said multiple vehicles were overturned, including tractor trailer trucks. The Oklahoma Highway Patrol announced online that one main thoroughfare, Interstate 40, has been shut down due to the threat.
KFOR television meanwhile reported extensive damage around the cities of El Reno and Yukon, with 22,000 customers without power.
The eye of one strong funnel cloud - nearly a mile (1.6km) wide - was barrelling toward downtown Oklahoma City to the south, according to KFOR.
The National Weather Service issued a tornado emergency for the city and some of its suburbs, hinting at the potential for casualties and large-scale damage.
Officials for Oklahoma City's Will Rogers World Airport said on Twitter that passengers had been evacuated to an underground tunnel.
"No flights are arriving," it added. "Please do not come to airport to pick-up until threat has passed."
The National Weather Service's Storm Prediction Centre in Norman, Oklahoma, issued a forecast for "a few strong to violent tornadoes, very large hail and intense damaging winds over parts of the Southern Plains to the Ozark Plateau". Forecasters said the hail could be larger than the size of a baseball, with wind gusts greater than 60 miles per hour.
The Moore tornado affected a total of 33,000 people, and had winds above 200 miles per hour.
With an average of 1,200 tornadoes per year, the United States is the most hurricane-prone country in the world. They are particularly prominent in the Great Plains states of Kansas, Oklahoma and Texas, as well as in Florida.
Southeastern Kansas, southwestern Missouri and central to northeastern Oklahoma were most likely to bear the brunt of the storm, according to the National Weather Service.
Severe storms were also forecast to strike across the upper to middle Mississippi Valley and the Midwest.