Hurricane Florence made landfall on Friday and has already caused widespread destruction and left more than 500,000 people without power.
FEMA administrator Brock Long told CBS News: “The inland coastal towns like New Bern are experiencing, basically, the ocean rising – what we have been saying, what forecasters have been predicting.
“Nine feet of storm surge. And our concern is that it is only going to get worst at this point.
“Because when a system like this stalls out, regardless of whether it is a category one or category four, it continues to just pump water into those back bay and inland areas.
“That coupled with the high tide that is going to be coming later today is just not setting up to be a good event for anybody.”
When asked what the Fema boss’ best advice was, he said he wishes people would “heed the warnings” and evacuate from the areas expected to be worse hit.
He added: “The way we support the search and rescue is that we try to pre-deploy thousands of people down, search and rescue team, swift water rescue teams, to help the heroes at the local level in the communities that are going through this to backfield their capability.
“What’s unfortunate is that these guys have to risk their lives to go in and save people that did not heed the warnings for whatever reason.”
The centre of Hurricane Florence came ashore at 7.15am EDT (12.15pm BST) near Wrightsville Beach close to Wilmington, North Carolina with sustained winds of 90mph (150kph), the National Hurricane Center said.
Hurricane Florence was downgraded to a category one hurricane on Thursday evening but is still packing 90mph winds after slowing to 6mph.
Florence has caused the evacuation of some 1.5 million people with millions more likely to see some impact from the howling winds.
The NOAA’s National Hurricane Centre (NHC) has warned multiple tornadoes could form within the area of North Carolina.
An official warning from the centre reads: “A few tornadoes are possible in eastern North Carolina today.”
Florence has also caused widespread travel chaos, with more than 1,500 flights cancelled in the worst hit states.
A spokeswoman at Charleston International Airport confirmed that all flights will be cancelled until at least Friday night.
While around half of flight departures and arrivals for Friday to Raleigh-Durham International Airport have also been cancelled.
Airlines are urging passengers to check their websites for more information regarding the storm.