(Updates with details of flood threats in Georgetown, S.C., and flooding in Wilmington, N.C.)
By Harriet McLeod and Gene Cherry
Sept 23 (Reuters) - Rain-swollen rivers in North and South Carolina kept rising on Sunday and were forecast to remain at flood level for days, the National Weather Service said more than a week after the landfall of Hurricane Florence, already blamed for at least 40 deaths.
As many as 8,000 people in and around Georgetown, South Carolina, have been "strongly urged" to evacuate flood-prone areas along the Waccamaw and Pee Dee rivers early this week, Georgetown County spokeswoman Jackie Broach-Akers told Reuters.
Emergency management officials began sending pre-recorded telephone messages to residents in harm's way over the weekend, and will probably start going door-to-door in the next few days, she said.
Authorities expect 5 to 10 feet (1.5 m to 3 m) of flooding in neighborhoods encompassing some 3,500 homes close to where the two rain-gorged rivers flow into Winyah Bay on the way to the Atlantic, Broach-Akers said. The flood zone includes Georgetown, at the rivers' confluence, and the coastal resort community of Pawleys Island.
The county plans to open emergency shelters at 7 a.m. on Monday, and hotels outside the flood zone in nearby Myrtle Beach are offering discounts for evacuees. Public schools will be closed until further notice, Broach-Akers said.
State transportation crews were working to erect temporary dams on either side of U.S. Highway 17, the main coastal route through the area, and National Guard engineers were installing a floating bridge at Georgetown in case the highway is washed out at the river.
About 100 miles (160 km) up the coast, a commercial section of downtown Wilmington, North Carolina, by the Cape Fear River was under a foot of water, with flooding expected to rise by a further 2 feet (0.61 m) with high tide on Sunday evening, city spokesman Dylan Lee said.
Flooding in Wilmington was expected to peak on Monday along the city's Water Street riverfront, where many businesses had stacked sandbags in advance, Lee said. But the city said its offices would reopen on Monday after having been closed for a week.
Nine days after Florence came ashore, the National Weather Service said flooding would likely persist in coastal parts of the Carolinas for days as the high-water crest of numerous rivers keeps moving downstream toward the ocean.
"This isn't over," said Bob Oravec, a meteorologist with the NWS' Weather Prediction Center. "All that water is going to take a good while to recede," he said. "Damage can still be done. It'll be a slow drop."
The storm dumped 30 to 40 inches (75 to 100 cm) of rain on the Wilmington area alone after making landfall nearby on Sept. 14.
Floodwaters have begun to recede farther inland.
That left hundreds of dead fish stranded on a highway near Wallace, about 35 miles (56 km) from the nearest beach, according to the Penderlea Fire Department, which posted video of firefighters hosing the fish off Interstate 40.
"Well, we can add 'washing fish off of the interstate' to the long list of interesting things firefighters get to experience!" the department said on Facebook.
Remnants of the once-mighty storm brought heavy rains across a wide swath of the country, prompting flood watches and warnings from Texas to Virginia and Maryland, at least through Monday, the weather service said.
About 5,000 people across North Carolina have been rescued by boat or helicopter since the storm made landfall, twice as many as in Hurricane Matthew two years ago, according to state officials. Thousands of people remained in shelters. (Reporting by Harriet McLeod in Charleston, S.C. and Gene Cherry in Raleigh, N.C.; Additional reporting by Rich McKay in Atlanta, Daniel Trotta in New York and Steve Gorman in Los Angeles; Editing by Daniel Wallis and Peter Cooney)