Emergency workers delivered truckloads of food and water to Wilmington, a city of 120,000 people cut off from the rest of North Carolina by Florence's still-rising floodwaters, as helicopters and boats pulled people from homes swamped by swollen rivers.
The deadly storm still had abundant rain and top winds around 50km/h early on Monday, and forecasters said it was expected to gradually pick up forward speed and complete a big turn towards the northeast, which is in for as much as 15cm of rain.
Flooding worries were increasing in West Virginia and Virginia, where roads were closed and power outages were on the rise. About 500,000 homes and businesses were in the dark.
The storm's death toll climbed to 18 as authorities found the body of a one-year-old boy who was swept away by floodwaters in North Carolina after his mother drove into floodwaters and lost her grip on him while trying to get back to dry land.
The head of the Federal Emergency Management Agency warned that other states, including West Virginia and Ohio, would be affected later in the week.
North Carolina emergency response officials tweeted that 23 truckloads of military meals and bottled water were delivered overnight to Wilmington. Residents waited for hours outside stores and restaurants for water and other basic necessities.
To the north in Pollocksville, Coast Guard members used a basket suspended from a helicopter to rescue a man from the roof of a flooded home.
About 115km away from the coast, residents near the Lumber River stepped from their homes directly into boats floating in their front yards.
Florence was still massive, despite being downgraded to a tropical depression from a once-fearsome Category 4 hurricane. Radar showed parts of the sprawling storm over six states, with North and South Carolina in the bull's-eye.
Victor Merlos was overjoyed to find a store open for business in Wilmington since he had about 20 relatives staying at his apartment, which still had power. He spent more than $US500 on cereal, eggs, soft drinks and other necessities, plus beer.
"I have everything I need for my whole family," Merlos said.
Julie Lamb, with her 15-month-old twins, stepped off a Coast Guard boat after being rescued from her parents' house, where the yard was submerged and water was still rising at Lumberton. Another boat was going back to get her husband, four-year-old daughter and their pug dog.
As rivers swelled, state regulators and environmental groups monitored the threat from gigantic hog and poultry farms in low-lying, flood-prone areas.
The industrial-scale farms contain vast pits of animal faeces and urine that can pose a significant pollution threat if they are breached or inundated by floodwaters.
Some stream gauges used to monitor river levels failed when they became submerged, but others showed water levels rising steadily, with forecasts calling for rivers to crest at or near record levels.
