More than 80,000 people were already without power as the storm approached, and more than 12,000 were in shelters.
"It truly is really about the whole size of the storm", said National Hurricane Center head Ken Graham.
Forecasters also said the Category 1 storm's extreme size meant it could batter the US East Coast with hurricane-force winds for almost a full day. "There is probably not a county or a person that will not be affected in some way by this very massive and violent storm".
More than 1.7 million people in the Carolinas and Virginia were warned to evacuate over the past few days, and the homes of about 10 million were under watches or warnings for the hurricane or tropical storm conditions.
Schools and businesses closed as far south as Georgia, airlines canceled more than 1,500 flights, and coastal towns in the Carolinas were largely emptied out.
Hurricane Florence is bearing down on the US East Coast as a Category 2 hurricane with winds up to 110mph - slower than yesterday but covering a wider area.
Twice a day for the past week, Michael Sprayberry, the Director of North Carolina's Division of Emergency Management has briefed officials working out of the sprawling glass and steel building that is serving as the state's emergency response hub ahead of Hurricane Florence.
But the storm still carried "very unsafe winds", the Center added.
Hurricane Florence is on a path of destruction that will put millions of people at risk and threaten billions of dollars in property damage, centered on the Carolinas, through this weekend. The baby's father was injured and taken to a hospital. Paramedics trying to reach her were blocked by debris. A 78-year-old man was electrocuted attempting to connect extension cords while another man died when he was blown down by high winds while checking on his hunting dogs, a county spokesman said.
Hurricane warnings and storm surge warnings were still in effect from South Santee River in SC to Duck in North Carolina and the Albemarle and Pamlico Sounds.
And about 46 miles north of Emerald Isle in New Bern about 150 people were waiting to be rescued from rising flood waters, WXII-TV reported. A town spokesman said between 60 and 75 people were awaiting rescue on Saturday.
"It's not the middle of a hurricane yet, so why not come for a beer?" said Waters, 54. "Inland flooding kills a lot of people, unfortunately, and that's what we're about to see", he said. "My wife's in a panic right now".
As the soil becomes saturated, gusty winds will topple trees and lead to widespread power outages. "We just bought a new house so I'm kinda nervous". "There is overwash but nothing we are not used to", she said. "This is a 500- or 1,000-year event".
North Carolina alone is forecast to get 9.6 trillion gallons, enough to cover the Tar Heel state to a depth of about 10 inches (25 centimeters). The figure for SC was 170,000. "Florence will then recurve across the western Carolinas and the central Appalachian Mountains early next week".
Florence was 155 miles (250km) east of Myrtle Beach in SC at 17:00 EDT (21:00 GMT), and is projected to make landfall on Friday at 08:00 local time.
Despite pleas from officials, some residents rejected calls to evacuate.
Florence diminished from hurricane strength as it came ashore on Friday, but the large storm's slow progress across the two states could leave much of the region under water in the coming days, according to forecasters.
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