After Helene, searches continue for scores of loved ones unaccounted for after devastating storm

As Helene swept through North Carolina last week, John Norwood and his fiancé, Julie le Roux, sought shelter at a neighbor's house.

As they attempted to wait out the worst of the storm, which made landfall in Florida as a Category 4 hurricane, a mudslide destroyed the home they had taken shelter in.

"We looked outside and there was a 30-foot-tall wall of water and rocks and tree debris just coming at us," Norwood told ABC News.

The debris knocked the house "straight down," flushing out those who had been huddled inside, he said, adding, "And we all got washed downriver." Norwood was rescued, but le Roux is still unaccounted for, he said. She's one of hundreds of people who are unaccounted for after the storm, according to officials.

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The storm was "unprecedented" for western North Carolina, requiring an "unprecedented response," Gov. Roy Cooper said Monday. At least 40 people were killed by the storm in Buncombe County, in the western part of the state, local officials said Monday.

Hundreds of people were missing or unaccounted for as of Monday throughout the southeastern United States, Homeland Security adviser Liz Sherwood Randall said as she gave a lengthy update on the federal response to Helene, including a warning that much is still unknown about the situation.

"When I said there could be up to 600 people lost my point was, there 600 people unaccounted for," Sherwood Randall said. "That's the number we're tracking right now and that we can essentially validate from multiple sources."

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But, she added, there was still uncertainty in that number. It included many who hadn't been heard from, but they may just be out of contact, she said.

"And as the president said this morning, we're very hopeful that some of those people just don't have cell phones working and actually are alive," she said.

Elsewhere in North Carolina, there were gas lines stretching from stations, as survivors waited for fuel. Officials were busy supplying water and ready-to-eat meals, Will Ray, the director of the state's Emergency Management agency, said.

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In Marion, a city in the state's hard-hit western area, rescuers used a pulley system to pull Norwood to safety, carrying him over rushing flood waters. A ceiling rafter had crushed his legs, he said, but at least he was rescued. He said he hasn't seen le Roux since the mudslide hit.

"I crawled around screaming, looking for her," he said as he fought back tears, "and I just couldn't find her."

ABC New's Katie Bosland, Kimberly Randolph and Kelly Hagan contributed to this report.