An ice storm heading for the central United States is threatening to cause power outages and create treacherous travel conditions on Friday and into the weekend, the National Weather Service said.

Ice, freezing rain and winter storm warnings were in effect for a large swathe of the Plains, from the Texas panhandle north into Iowa and east through central Indiana, the Weather Service said in an advisory.

"Significant amounts of ice accumulations will make travel dangerous or impossible," the weather service said. "Travel is strongly discouraged. Commerce will likely be severely impacted."

Ice accumulation could be more than half an inch (1 cm) depending on local temperatures, creating slick roadways especially on bridges and overpasses, and possibly causing scattered power outages across the region, the service said.

Oklahoma Governor Mary Fallin declared a state of emergency for the entire state ahead of the storm.

"Emergency personnel are coordinating with state and local officials to ensure we are prepared and ready for whatever comes our way," said Fallin.

A handful of public schools, government offices and universities in Idaho, Oklahoma and other parts of the central region were shut down on Friday or had delayed openings due to the impending storm.

Parts of the region could also see as much as 3 inches (8 cm) of snow later in the weekend, according to the forecast.

“The best thing to do when it's icy is stay home,” the Oklahoma Department of Emergency Management said, adding that those who do venture out should heed the advice: “Ice and snow, take it slow.”

There were no immediate reports of major injuries or deaths as a result of the winter storm.