Evacuations are underway in North and South Carolina ahead of the arrival of a potentially catastrophic category four storm.
Hurricane Florence is bearing down on the east coast of the US with sustained wind speeds of 140mph.
The US National Hurricane Centre (NHC) has warned locals it could be "extremely dangerous" – with a state of emergency declared in a number of states.
The hurricane is expected to make landfall on Thursday.
Supermarket shelves have been stripped and cars stocked up with petrol as thousands prepare to flee the hurricane’s path.
It will move over the southwestern Atlantic Ocean between Bermuda and the Bahamas on Tuesday and Wednesday, by which time forecasters believe it could be a category five storm.
The first effects are already being seen, with rip currents having roared into beaches, causing seawater to flow over a state highway.
To the incredible citizens of North Carolina, South Carolina and the entire East Coast - the storm looks very bad! Please take all necessary precautions. We have already began mobilizing our assets to respond accordingly, and we are here for you! pic.twitter.com/g74cyD6b6K
— Donald J. Trump (@realDonaldTrump) September 10, 2018
NHC director Ken Graham said the storm is expected to linger over North and South Carolina after it makes landfall.
Approximately one million people have been told to evacuate in both states, with people situated well inland warned that they could lose power and face flooding.
Mr Graham said: "It's not just the coast. When you stall a system like this and it moves real slow, some of that rainfall can extend well away from the centre."
Half a dozen nuclear power plants could find themselves in the path of the storm, as could pits holding industrial waste.
Here are the Key Messages from the 11 pm advisory for Hurricane #Florence. pic.twitter.com/XzGiOhaGHy
— National Hurricane Center (@NHC_Atlantic) September 11, 2018
Maryland Governor Larry Hogan has declared a state of emergency and said officials were "preparing for the potential of historic, catastrophic and life-threatening flooding."
The mayor of Richmond in Virginia, Levat Stoney, has also declared a state of emergency and has urged residents to gather non-perishable food, water, torches, and batteries.
As for fuel, one gas station owner in Wilmington, North Carolina, told the Reuters news agency she had seen triple the usual number of customers as locals are "getting frantic" over the potential impact of the storm.
My people just informed me that this is one of the worst storms to hit the East Coast in many years. Also, looking like a direct hit on North Carolina, South Carolina and Virginia. Please be prepared, be careful and be SAFE!
— Donald J. Trump (@realDonaldTrump) September 10, 2018
US President Donald Trump - who was criticised for his response to the deadly Hurricane Maria in Puerto Rico last year - has tweeted that the government "stands by, ready to assist 24/7."
In a further post, he said he had been told that Florence was "one of the worst storms to hit the east coast in many years" and was "looking like a direct hit on North Carolina, South Carolina and Virginia."
"Please be prepared, be careful and be safe," he added.
Hurricanes are powered by warm oceans, and Florence is moving over waters in areas where temperatures are peaking at about 30C (86F).