Hurricane Florence rolled ashore in North Carolina with howling 145kph winds and a terrifying storm surge early yesterday.
Buildings were splintered and hundreds of people were trapped by high water as they settled in for what could be a long and extraordinarily destructive drenching.
In Wilmington, a mother and child were killed when a tree fell on their house.
More than 60 people had to be pulled from a collapsing motel and hundreds more were rescued elsewhere from rising water.
Others could only wait and hope someone would come for them.
"We are coming to get you," the city of New Bern tweeted at around 2am. "You may need to move up to the second storey, or to your attic, but we are coming to get you."
As the giant, 650km-wide hurricane pounded away, it unloaded heavy rain, flattened trees, chewed up roads and knocked out power to more than 600,000 homes and businesses.
The biggest danger, as forecasters saw it, was not the wind but the water.
The storm surge along the coastline brings the prospect of up to a metre of rain over the coming days, which could trigger catastrophic flooding inland in a slow-motion disaster.
By early afternoon, Florence's winds had weakened to 120kph, just barely a hurricane and well below the storm's terrifying category four peak of 225kph earlier in the week.
However, the hurricane had slowed to a crawl as it traced the North Carolina-South Carolina shoreline, drenching coastal communities for hours.
The town of Oriental received more than 45cm of rain only a few hours into the deluge, while Surf City had 35cm and it was still coming down.
"Hurricane Florence is powerful, slow and relentless," North Carolina Governor Roy Cooper said.
"It's an uninvited brute who doesn't want to leave."
Mr Cooper said the hurricane was "wreaking havoc" on the coast and could wipe out entire communities as it makes its "violent grind across our state for days".
He said parts of North Carolina had seen storm surges - the bulge of seawater pushed ashore by the hurricane - as high as three metres.
Florence made landfall as a category one hurricane at 7.15am local time at Wrightsville Beach, a few kilometres east of Wilmington, coming ashore along a mostly boarded-up, emptied-out stretch of coastline.
It was expected to begin pushing its way westward across South Carolina later in the day, in a watery siege that could go on all weekend.
For people living inland in the Carolinas, the moment of maximum peril from flash flooding could arrive days later, because it takes time for rainwater to drain into rivers and for those streams to crest.
Preparing for the worst, about 9,700 National Guard troops and civilians were deployed with high-water vehicles, helicopters and boats that could be used to pluck people from the flood waters.
Authorities warned, too, of the threat of mudslides and the risk of environmental havoc from flood waters.
North Carolina alone is forecast to receive 9.6 trillion gallons of rain, enough to cover the state to a depth of about 25cm.
In New Bern, flooding trapped many, and Mayor Dana Outlaw said that about 200 people had been rescued by 5am.
Restaurant owner Tom Balance had decided against evacuating his home and was alarmed to see the water getting higher and higher.
Six sheriff's officers came to his house to rescue him, but he did not need to leave as the water was dropping by then.
Still, he said: "I feel like the dumbest human being who ever walked the face of the Earth."