The head of the Federal Emergency Management Agency warned those living in the southeastern United States to listen to evacuation orders as Hurricane Irma barrels toward Florida and said the Category 5 hurricane will be "truly devastating."

"Bottom line is the majority of people along the coast have never experienced a major hurricane like this," FEMA Administrator Brock Long told CNN on Thursday. "It will be truly devastating."

Hurricane Irma is expected to make landfall in South Florida on Sunday, and government officials have already issued mandatory evacuation orders for the Florida Keys, as well as parts of Miami and Fort Lauderdale.

Long said he expects evacuation orders to be issued for Georgia, South Carolina, and North Carolina within the next two days as the storm moves toward the U.S.

"The entire southeastern United States better wake up and pay attention," he said.

Hurricane Irma tore through the Caribbean on Wednesday with sustained winds of 180 miles per hour, and widespread damage was reported on the islands of Barbuda and St. Martin. The storm hit Puerto Rico on Wednesday night, leaving more than 1 million people on the island without power.

The storm will be the first Category 5 hurricane to hit the mainland U.S. since Hurricane Andrew in 1992.

Hurricane Irma will hit Florida less than two weeks after Hurricane Harvey made landfall in southeastern Texas, bring record rainfall and catastrophic flooding to parts of the state. FEMA officials are currently responding to both storms, but Long said he wasn't worried about funding in the face of the two hurricanes.

"I'll never allow paperwork and money to get in the way of saving lives," Long said.