A dangerous kilometre wide tornado struck near Oklahoma City today, part of an extreme weather system moving through the central U.S. and stretching from north Texas to Minnesota.

At 6:12 p.m. Central Standard time, the National Weather Service office in Norman, Oklahoma issued an insistent alert on Twitter about tornado striking Pink, a town on the edge of Oklahoma City.

“Large tornado west of Pink!” the post read. “Take cover RIGHT NOW in Pink! DO NOT WAIT!”

The storm system had been building for hours when a “large tornado” touched down near Wichita, Kansas at 3:45 Central Standard time, according to a weather service alert.

“Exceptionally powerful, severe thunderstorms capable of destructive hail as large as baseballs … are likely … especially over southeast Kansas this evening,” another NWS advisory warned.

Kansas, Missouri, Oklahoma and Nebraska are all in the path of the storm system, which could produce up to150kph inds, baseball-sized hail and violent tornadoes in some areas.

The storm is so large and severe it prompted an unusually blunt National Weather Service warning.

“You could be killed if not underground or in a tornado shelter,” the advisory reads. “Complete destruction of neighborhoods, businesses and vehicles will occur. Flying debris will be deadly to people and animals.”

A tornado also touched down in southwest Wichita at 3:45 p.m. Central time, moving northeast at about 35 miles per hour toward Topeka, said Pat Slattery, National Weather Service spokesman for the U.S. Central region, which covers 14 states.

In northeast Oklahoma, the Lincoln County sheriff’s office reported three tornado touchdowns in the region.

Slattery said the potential severity of the storm prompted the weather service to issue the stark advisory, which is part of a new “impact-based warning system” being tested in the U.S. Central region, in the wake of a violent tornado that struck Joplin, Missouri on May 22, 2011, killing 158 and wounding hundreds more.

Slattery said the new, more urgent advisory is reserved for severe tornadoes with the potential to form into super cell storms, which produce powerful winds and flash flooding. Super cells are considered to be the most dangerous of four categories of storms because of the extreme weather they generate.

A recent National Oceanic and Atmospheric Administration assessment of the Joplin storm found that “when people heard the first tornado warning, they did not immediately seek shelter. They looked for a secondary source to confirm the tornado,” Slattery said. “That got some people killed.”

Weatherwatch & CNN