Search-and-rescue teams who have already saved hundreds of people scoured the mountains of western North Carolina for more survivors, working amid washed-out roads, smashed bridges and felled power lines following Hurricane Helene.

While the death toll stands at 162, CNN reported, citing state and local officials, it is expected to rise once rescue teams reach isolated towns and telecommunications are restored.

The death toll rose after North Carolina's Buncombe County reported 57 dead on Tuesday, up from 40 a day earlier.

The mountainous area, including the county seat of Asheville, bore the brunt of the storm, which US Homeland Security Secretary Alejandro Mayorkas said was of "historic magnitude".

Recovery will involve a "multibillion-dollar undertaking" lasting years, Mayorkas told reporters at the White House.

President Joe Biden vowed to "jump start this recovery process" after speaking with governors and other leaders in the impacted areas.

"People are scared to death. People wonder whether they're going to make it. We still haven't heard from a whole lot of people. This is urgent," Biden said.

Hundreds of people have been reported missing, a number that is expected to decline as more telecommunications come back online and emergency workers can get into remote areas.

The North Carolina National Guard has rescued over 500 people, deployed helicopters to ferry supplies and rescue workers, and rescued survivors and pets along the way, Major General Todd Hunt told a separate press briefing.

Power outages were down to 420,000 from a peak of one million in North Carolina, with all but two hospitals in the west of the state back on commercial power, said state Health Department Secretary Kody Kinsley. Access to public drinking water systems was scarce.

In all, 1.5 million homes and businesses in six states from Florida to West Virginia remained without power on Tuesday morning, according to the website Poweroutage.us.

With AAP.