"I've lived in North Carolina my entire life, and I've seen a lot of bad storms, a lot of bad hurricanes. But this is absolutely the worst," he said.
"I thought that [Matthew] would be the worst I've ever saw in my life. But this [Florence] certainly surpasses that," he said.
Florence made landfall on Thursday as a Category 1 hurricane at Wrightsville Beach, North Carolina, a resort town just east of the state's eighth-largest city, Wilmington, which has been completely cut off by surrounding floodwaters.
At least 18 storm-related deaths have been reported in the region.
The threat of more flooding continues as rivers in the Carolinas begin to crest in the coming days, even as the remnants of Florence tracked northward after dumping days of drenching rain.
Fountain, 51, said about 300,000 Duke Energy households and businesses remained in the dark as of Monday morning.
"With 1.4 million customers having been impacted, we're pleased with the restoration progress ... especially under such challenging conditions," he said. "But we've got a lot more work to do."