Meanwhile there are reports of serious looting on the hurricane-hit Caribbean island of St Martin.
Hurricane Irma has left a trail of destruction in the Caribbean, affecting an estimated 1.2m people.
It has been downgraded to a category four storm, but officials warn that it remains "extremely dangerous".
The US National Weather Service says that Irma was expected to bring wind speeds of around 165mph (270km/h) over the weekend.
Some 500,000 people were told to leave south Florida with Irma due on Sunday.
"Hurricane Irma continues to be a threat that is going to devastate the United States in either Florida or some of the southeastern states," Fema administrator Mr Long said.
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