A mother and her baby were killed in North Carolina when a tree fell on their house, while Hurricane Florence crashed in the state, flooding the streets with torrential rain and a strong storm surge.
Police say the couple, in Wilmington, were the first confirmed deaths directly related to the storm, which touched down on Friday.
The father of the child was taken to the hospital.
In Pender County, North Carolina, a woman died after she suffered a heart attack and paramedics were unable to contact her because of blocked roads, authorities said.
After making landfall, Florence slowed down to a rate that meant it would plague the area with days of flooding.
The wall of water pushed from the Atlantic "overwhelmed" New Bern, a city of some 30,000 people at the confluence of the Neuse and Trent rivers, said North Carolina Governor Roy Cooper.
"The sun came out this morning in an extremely dangerous situation and is going to get worse," Cooper told a news conference in the state capital, Raleigh.
"For those on the path of the storm, if you can hear me, please remain protected in your place."
Cooper said Florence "would continue her violent routine throughout the state for days."
More than 60 people, including many children and pets, had to be evacuated from a hotel in Jacksonville, North Carolina, after strong winds collapsed parts of the roof.
The center of the eye of the hurricane reached the coast at 7.15 a.m. local time, near Wilmington, with sustained winds of 150 km / h, said the National Hurricane Center.
At 1.50pm, local time, the winds had dropped to 120km / h and the center was moving westward at a speed of 10km / h.
It is expected that parts of North Carolina and the South get up to one meter of rain.
As of Friday morning, Atlantic Beach, a city on the islands of the state's Outer Banks, had already received 76 cm of rain, the US Geological Survey said.
Authorities in New Bern said that more than 100 people had to be saved from the floods and that the downtown area was underwater.
The town's public information officer, Colleen Roberts, told CNN that 150 people were waiting to be rescued.
"WE'RE GOING TO ARRIVE," officials in the city of New Bern told Twitter.
"It is possible that you have to move on to the second story, or to your attic, but WE WILL GET YOU".
Video reports from several cities in the Carolinas showed that emergency personnel moved forward through flooding in residential neighborhoods.
More than 634,000 homes and businesses were without power in North Carolina and South Carolina early Friday, company officials said.
It is expected to move through parts of southeastern North Carolina and eastern South Carolina on Friday and Saturday, and then head north over the Western Carolinas and the Central Appalachian Mountains early next week. .
A significant weakening is expected during the weekend.