Though Florence's shrieking winds diminished from hurricane force as it came ashore, forecasters said the sheer size of the 350-mile-wide storm and its painfully slow progress across North and SC in the coming days could leave much of the region under water.
"We've rescued over 100 people in New Bern, N.C.; people from Jacksonville, N.C., had to rescued from a hotel", Cooper said, describing efforts to save people in towns north of Wilmington where high floods have already hit.
Police in Wilmington confirmed the mother, Lesha Murphy-Johnson, and baby Adam died, with the tot's father rescued and rushed to the hospital. Another person died from a cardiac arrest when emergency services could not reach her, due to downed trees blocking their path. Few people had ventured out - most were heeding warnings from officials to stay inside.
U.S. media later said a second man in Lenoir County died after heavy winds knocked him down as he tried to check on his dogs.
President Donald Trump, left, talks about Hurricane Florence during a briefing in the Oval Office of the White House.
Resident Jay Manning said he and his wife watched with alarm as water filled the street. "You may need to move up to the second story, or to your attic, but WE ARE COMING TO GET YOU", the authorities in New Bern said on Twitter. "My wife's in a panic right now".
"We've got nearly 20,000 people in 157 shelters", Cooper said.
Florence flattened trees, crumbled roads and the assault wasn't anywhere close to being over, with the siege in the Carolinas expected to last all weekend. "This is a 500- or 1,000-year event".
Florence was a Category 3 hurricane on the five-step Saffir-Simpson scale with 120-mph winds on Thursday.
Tropical storm Florence lumbered inland on Saturday, knocking down trees, flooding rivers, and dumping torrents of rain in the Carolinas, where five people have died.
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. About 150 more had to wait to be rescued as conditions worsened.
The National Hurricane Center said the storm would dump as much as 30 to 40 inches (76-102 cm) of rain on the southeastern coast of North Carolina and part of northeastern SC, as well as up to 10 inches (25 cm) in southwestern Virginia.
It was downgraded to Category 1 before coming ashore on Friday near Wrightsville Beach, near Wilmington. In neighboring SC, 165,000 customers are without power, officials said. Trump plans a visit to the region next week.
Florence will continue to move very slowly to the southwest on Saturday, which in turn will drag the axis of heavy rain bands to the southwest as well.
Forecasters warned that drenching rains of 30 centimetres to 1 metre as the hurricane-turned-tropical storm crawls westward across North and SC could trigger epic flooding well inland over the next few days. Its westward motion is expected to continue through Saturday. Florence was one of two major storms threatening millions of people on opposite sides of the world.
Super Typhoon Mangkhut tore through the northern tip of the Philippines on Saturday packing winds of more than 200 km per hour (124 mph) along with torrential rain, killing three people and causing floods, landslides and power outages.