The head of the Federal Emergency Management Agency said U.S. officials were preparing a massive response to Hurricane Irma, which is set to hit Florida as early as Saturday.

"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 Brock Long said at a news briefing on Friday.

He was quoted by Reuters as warning that parts of Florida would be out of electricity for days if not longer and that more than 100,000 people may need shelter.