The storm killed at least 89 people, according to state and local officials in South Carolina, Florida, Georgia, North Carolina and Virginia.
Officials feared still more bodies would be discovered.
Damage estimates ranged from $US15 billion to $US100 billion ($A22 billion to $A145 billion), insurers and forecasters said over the weekend.
Property damage and lost economic output will become clearer as officials assess the destruction.
— USCGSoutheast (@USCGSoutheast) #HurricaneResponse—Yesterday, @USCG crews and partner agencies continued search and rescue efforts after #HurricaneHelene in Keaton Beach, Florida. DVIDS download: https://t.co/vQjCG7s4rD#USCG #coastguard #helene pic.twitter.com/tji530e6lCSeptember 29, 2024
North Carolina governor Roy Cooper on Sunday said the state's death toll rose to 11 people.
All roads in the western end of the state should be considered closed and will take months to repair, he said.
Food and water is being airlifted to those areas.
"This is an unprecedented tragedy that requires an unprecedented response," Cooper said at a press conference.
In Flat Rock, North Carolina, there were widespread blackouts and people waited hours in line for petrol.
Electric Vehicles that have been flooded in saltwater can catch fire. If you evacuated and left an electric vehicle or golf cart in your garage or under a building and you are not able to get to it or move it, we want you to let us know. /1 — Pinellas County (@PinellasGov) pic.twitter.com/dpfiXRAGuRSeptember 28, 2024
"Grocery stores are closed, cell phone service is out," Chip Frank, 62, said as he entered his third hour waiting in line.
"It all depends on these gas stations. You're not going to be able to go nowhere, and it's just a scary feeling."
The storm has damaged water systems, communications and critical transportation routes across the region, according to the Federal Emergency Management Agency.
The Army Corps of Engineers will start assessing damage to water systems on Sunday to help them get back online, FEMA said.
About 2.7 million customers remained without power on Sunday, a US Energy Department official said, down 40 per cent from Friday after unprecedented storm surges, ferocious winds and perilous conditions extended hundreds of kilometres inland.
Days of driving rain followed after Helene slammed into Florida's Gulf Coast on Thursday night, destroying homes that had stood for decades.
Eleven people died in Florida, Governor Ron DeSantis said on Saturday in the Gulf Coast city of Perry.
Some of the worst rains hit western North Carolina, where almost 76cm fell on Mount Mitchell in Yancey County, the National Weather Service's Weather Prediction Center reported.
Water washed over Lake Lure Dam in Rutherford County and people in and around Chimney Rock described the village's downtown as washed out.
Images showed inches of mud and sediment, uprooted trees and snapped telephone poles, and buildings turned into debris.
Just to the south in eastern Tennessee, Greene County officials worried that the Nolichucky Dam was on the brink of failure but the Tennessee Valley Authority reported that it was stable and secure.
"As we continue to support response and recovery efforts, we will make sure that no resource is spared to ensure communities can quickly begin their road to rebuilding," US President Joe Biden said in a statement on Sunday.
South Carolina recorded the highest death toll, with local authorities counting 24 fatalities, with falling trees contributing to many of them.
Seventeen people, including children, died in Georgia, Governor Brian Kemp said after viewing damage in Valdosta.
