- Video report by ITV News Washington Correspondent Robert Moore
Epic flooding is feared in parts of North and South Carolina and Virginia as tropical storm Florence moves inland from the US East Coast.
The storm could dump as much as a metre of water in some places, forecasters predict, with four deaths already attributed to the weather phenomenon.
Florence was downgraded from a hurricane to a tropical storm on Friday, with winds at one point reaching up to 90mph.
A mother and child were among those killed when a tree fell on their home in North Carolina.
The Wilmington Police Department confirmed the pair had died, while the child's father had to be taken to hospital for treatment.
Meanwhile, North Carolina’s governor’s office said a third person was killed while plugging in a generator, and the storm is believed to have been a factor in the death of another woman who suffered a heart attack.
By early evening on Friday, Florence had been downgraded to a tropical storm - though the National Hurricane Centre said it was still "life-threatening".
Hundreds of thousands of homes were left without power as the storm pounded the region, leaving officials frantically preparing for what they called "once-in-a-millennium" flooding.
North Carolina Governor Roy Cooper warned people in the state that relentless rain was set to continue through the weekend.
"Rivers are rising to dangerous levels," he said, calling it a "once-in-millennium rain event" in some areas.
"Stay indoors, don't drive through water, don't use a generator indoors, don't fly drones," he added.
More than 60 people had to be evacuated from a motel at risk of collapse in Jacksonville. Parts of buildings ripped apart by the storm flew through the air.
Authorities in the North Carolina city of New Bern said there are around 150 people waiting to be rescued from rising flood waters.
The US National Hurricane Centre said that a gauge in Emerald Isle, North Carolina, recently reported 6.3ft of inundation. Emerald Isle is about 84 miles north of Wilmington.
Screaming winds bent trees and led to near-horizontal rain as Florence’s leading edge whipped the Carolina coast to begin an onslaught that could last for days, leaving a wide area underwater from both heavy downpours and rising seas.
The storm’s intensity diminished as it neared land, with winds dropping to around 90mph.
Governor Cooper warned of an impending disaster.
He said: “The worst of the storm is not yet here but these are early warnings of the days to come.
“Surviving this storm will be a test of endurance, teamwork, common sense and patience.”
Mr Cooper requested additional federal disaster assistance in anticipation of what his office called “historic major damage” across the state.
More than 505,000 homes and businesses were already without power on Friday morning, as the storm began buffeting the coast.
Energy companies warn up to three million homes and businesses were at risk of losing electricity as more than 12,000 seek safety in shelters.
Another 400 people were in shelters in Virginia, where forecasts were less dire.
Prisoners were affected, too. North Carolina corrections officials said more than 3,000 people were relocated from adult prisons and juvenile centres in the path of Florence, and more than 300 county prisoners were transferred to state facilities.
Officials said some 1.7 million people in the Carolinas and Virginia were warned to evacuate, but it was unclear how many did.
The homes of about 10 million people were under watches or warnings for the hurricane or tropical storm conditions.
Forecasters said conditions would deteriorate as the storm pushes ashore near the North Carolina-South Carolina line and makes its way slowly inland.
Its surge could cover all but a sliver of the Carolina coast under as much as 11ft of ocean water, and days of downpours could unload more than 3ft of rain, touching off severe flooding.
Although it was once a Category 4 hurricane with winds of 140mph, the hurricane was downgraded to a Category 1 on Thursday night.
Forecasters said that given the storm’s size and sluggish track, it could cause enormous damage similar to what the Houston area saw during Hurricane Harvey just over a year ago, with floodwaters swamping homes and businesses.
As Florence drew near, President Donald Trump tweeted that Fema and first responders are “supplied and ready”, and he disputed the official conclusion that nearly 3,000 people died in Puerto Rico, claiming the figure was a Democratic plot to make him look bad.
Not everyone was taking Florence too seriously: About two dozen locals gathered on Thursday night behind the boarded-up windows of The Barbary Coast bar as Florence blew into Wilmington.
“We’ll operate without power; we have candles. And you don’t need power to sling booze,” said owner Eli Ellsworth.
Others were at home hoping for the best.