President Donald Trump warned on Friday that "Hurricane Irma is of epic proportion," and promised that the government "is ready."

Trump made his statement on Twitter after the head of the Federal Emergency Management Agency warned that the Category 4 Hurricane Irma will devastate part of the United States.

Hurricane Irma is of epic proportion, perhaps bigger than we have ever seen. Be safe and get out of its way,if possible. Federal G is ready!

The monster storm smashed across Carribean islands as it moved from the Atlantic. South Florida was bracing for a direct hit as early as Saturday. The storm comes on the heels of Hurricane Harvey, which left a destructive path through Texas.

Trump said the Coast Guard is among the agencies ready to help.

Our incredible U.S. Coast Guard saved more than 15,000 lives last week with Harvey. Irma could be even tougher. We love our Coast Guard!

He urged people in the path of Irma to obey local orders.

I encourage EVERYONE in the path of #HurricaneIrma to heed the advice and orders of local & state officials!

Earlier Friday, FEMA Administrator Brock Long warned at a news conference that parts of Florida would be out of electricity for days, if not longer, and that more than 100,000 people may need shelter.

"Hurricane Irma continues to be a threat that is going to devastate the United States in either Florida or some of the Southeastern states," Long said.

He warned people not to ignore evacuation orders.

"They need to get out and listen and heed the warnings," Long said.

_ Reuters contributed to this story