Hundreds of people remain missing after catastrophic flooding decimated towns, destroyed roads and cut off power for more than a million homes in the US’s south-east.

The death toll has continued to rise since Hurricane Helene – which was later downgraded to a tropical storm – tore across the region.

As of Tuesday, 135 people had been confirmed dead across six states, a figure that is expected to grow.

At least 40 of those dead were in the west of North Carolina, where 300 roads remain closed, hampering recovery operations, as well as the delivery of much needed food and water.

There was perhaps nowhere harder hit than Buncombe County, an area in the west of the state that includes the city of Asheville.

“We have biblical devastation,” Ryan Cole, an emergency official in the county, told the BBC on Monday. “This is the most significant natural disaster that any one of us has ever seen.”

President Joe Biden is expected to visit the state on Wednesday.

The president said he would visit Georgia and Florida “as soon as possible” to survey damage there as well.

Vice-president Kamala Harris, the Democratic presidential nominee, will visit Georgia to tour the storm damage there, cancelling a previously scheduled campaign appearance in Pennsylvania.

Though some of the floodwaters in the region have receded, large swathes of North Carolina remain immobilised by the effects of the storm.

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The extreme weather has also forced the closure of quartz mines in Spruce Pine, a tiny town about an hour north-east of Asheville, home to the world’s largest-known source of high-purity quartz.

The Spruce Pine quartz is critical for the production of semiconductors – the foundation of modern computing, necessary for devices like laptops and smartphones to function.

“It does boggle the mind a bit to consider that inside nearly every cell phone and computer chip you’ll find quartz from Spruce Pine,” Rolf Pippert, mine manager at The Quartz Corp, a leading supplier of high-quality quartz, told the BBC in 2019.

Mitchell County – which contains Spruce Pine – sits about 96km (60 miles) from Buncombe. It was hammered with more than 2ft (609mm) of rain between Tuesday and Saturday, the Associated Press reported.

As of Monday, officials from Mitchell County – where Spruce Pine sits – said in a statement that the county had “no electricity service, cell service, or internet connectivity”.

“Mitchell County experienced a catastrophic 500-year flood,” Mitchell County said. “A good bit of the county infrastructure has been either damaged or destroyed by floodwaters and uprooted trees and downed power lines caused by the storm.”

Both Sibelco and The Quartz Corp said they stopped operations on Thursday, the day before the centre of Helene passed over Mitchell County.

In separate statements, both companies said their priority was the health and safety of their employees.

In an email to the BBC, Quartz Corp’s head of communication May Kristin Haugen said it was “impossible” to determine when they would resume operations.

“We are currently assessing the damage at all plants but our ability to operate again will also greatly depend on surrounding infrastructure,” she said.

Despite the closures, Ms Haugen said she was not concerned about shortages in the short or medium term. “Everybody has learnt through Covid the importance of sizeable safety stocks,” she said.