Hurricane Helene's impact on South Carolina has been "devastating," and the storm has claimed the lives of 25 people in the state, Gov. Henry McMaster said Sunday.

"We don’t want to lose any more," McMaster said.

Nearly 1.3 million customers lost power in South Carolina at Helene's peak. As of Sunday afternoon, more than 800,000 customers remain in the dark.

The governor emphasized that power companies are working around the clock to restore electricity. Thousands of workers are on the ground, but downed trees tangled in power lines are delaying efforts, he said.

-ABC News’ Jason Volack

FEMA Director Deanne Criswell said the agency is sending more search and rescue teams to western North Carolina, where residents are facing "historic" flooding from Hurricane Helene.

"I don't know that anybody could be fully prepared for the amount of flooding and landslides that they are experiencing right now. But we have had teams in there for several days. We're sending more search and rescue teams in there," Criswell told CBS' "Face the Nation."

Gov. Roy Cooper described Hurricane Helene’s damage in western North Carolina as "catastrophic."

"This unprecedented storm dropped from 10 to 29 inches of rain across the mountains, leading to life-threatening floods and landslides," he said Sunday.

Water systems have been impacted and some roads have washed away, hampering the ability for officials to set up food and water distribution sites.

"We have sent bottled water in, but we also have the Army Corps of Engineers that's getting ready to start assessments today to see what we can do to help get those water systems back online quickly," Criswell said.

"We're also moving in satellite communications, Starlink satellites, into the area to help facilitate the lack of communication that part of the state is experiencing," Criswell added.

-ABC News’ Michelle Stoddart and Jason Volack

Seventy-three people remain unaccounted for in Unicoi County, Tennessee, in the wake of Hurricane Helene’s devastation, including those needing welfare checks, county officials said.

One search and rescue team discovered a casket while navigating a debris field, Unicoi County Mayor Garland "Bubba" Evely said.

"We are working with the William Jenkins Forensic Center for identification and family notification. However, there are no confirmed deaths related to the floods at this time," Everly said.

-ABC News’ Jason Volack

In hard-hit Buncombe County, North Carolina, which encompasses Asheville, Sunday’s clear skies "will help our crews continue intense rescue and recovery operations," county manager Avril Pinder said.

"We’re still dealing with mudslides, flooded areas and stranded individuals. Our priority remains saving every person we can," she said. "Wellness checks will have to wait."

Ten people in Buncombe County have been killed by Hurricane Helene, Sheriff Quentin Miller said.

"Our hearts are broken," he said. "We’ve lost friends, family and neighbors."

Several roads have washed away, hampering the ability for officials to set up food and water distribution sites.

"We’ve got private helicopters dropping food at key locations," said Anthony Penland, fire chief in Swannanoa, just outside of Asheville. "But we still need the community to come together and help one another."

"We intend to have water services available soon, but we're asking for one more day of patience," Pinder said.

"We’re all going to need to lift each other up to get through this," she added.

-ABC News’ Jason Volack

Asheville Assistant City Manager Ben Woody stressed the importance of the North Fork Water Treatment Plant, which supplies 80% of Asheville's water.

"Restoring service after the storm depends on this system," Woody said.

He detailed storm damage, including the washout of two major waterlines -- a 36-inch and a 24-inch -- mirroring a 2004 disaster.

The city’s top repair priority is a 36-inch bypass line installed after that event, he said.

"If we get this bypass online, we can restore 80% of the system," Woody said, noting progress as of October 3.

Woody also confirmed the Mills River Water Treatment Plant, serving South Asheville, Buncombe and parts of Henderson County, is fully operational, producing five million gallons per day—about 20% of the system’s needs.

"There’s still a long way to go," he added.

-ABC News' Jason Volack