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Storm watchers in the US are warning of a major tornado outbreak this weekend after part of Oklahoma was hit by a twister that ripped roofs from buildings and tore down power lines.
Residents were told to take cover in basements as the tornado struck in Norman, a town of 110,000, on Friday.
Trees were uprooted and City Hall was among the buildings damaged.
Forecasters say another swarm of twisters may be on the way, with heavily populated areas such as Oklahoma city and Wichita, in Kansas, among the areas at risk.
Steve Weiss, of the National Storm Prediction Centre, said atmospheric conditions for the weekend are similar to those that caused deadly storms in parts of the midwest and southeast in early March.
He said: "We see potentially some ... very damaging tornadoes."
The biggest storms are expected on Saturday and could continue after dark. Oklahoma has activated an emergency operations centre in anticipation.
Kurt Van Speybroeck, of the National Weather Service, said: "The really dangerous part is that it looks like it's going to be overnight.
"It's a really bad combination to get tornadoes at night because they're harder to see."
Twisters have been blamed for 57 deaths in the US so far this year after the tornado season started early.
