The huge tornado that struck the town of Moore, Oklahoma, on Monday was given a preliminary rating of at least EF4, or the second highest strength level, with winds of up to 200 miles per hour (321 kph), a US government agency said.
"We believe it was at least an EF4," said Keli Pirtle, spokeswoman for the National Weather Service Storm Prediction Center in Norman, Oklahoma.
The Fujita scale rates tornadoes from weakest (EF1) to strongest (EF5). An EF4 tornado can blow away a well-constructed wood or brick home. A final rating will not be known until teams have examined the damage.