The National Weather Service (NWS) warned that the storms would drop "a few tornadoes near an outflow boundary where wind shear is very favorable for rotation. Other scattered severe storms are possible farther southward through Oklahoma this afternoon and evening."

Local television KWTV filmed the large tornadoes, near the towns of Hennessey and Bison, around 2000 GMT, perched close to the system in a helicopter as tornado funnel clouds -- black shadows against a grey-sky backdrop -- churned up ground below, sending rocks, splinters of wood and other debris skyward.

There were no immediate reports of injuries or fatalities.

A NWS spokesman in Norman, Oklahoma told AFP the "well-developed" tornadoes hit Kingfisher and Garfield counties.

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