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 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.

On Tuesday afternoon, an old flat red-brick building in Statesville, two hours east of the city of Asheville, North Carolina, was filled with roughly 50 volunteers working to get supplies to the hardest-hit areas of the state.

The previously empty room now had stacks of items, ranging from toilet paper to dog food. Several cases of much-needed water were also piled around, towering as high as some of the volunteers.

“This all happened since yesterday at 11:00,” Beth Kendall, who helped organise the efforts, told the BBC, pointing around the small, cramped space covered in piles of donated goods.

“The community response has just been amazing.”

Many have seen reports of people still missing, Ms Kendall said.

“On social media, you see lots of people that you know that are still looking for loved ones.”

Others shared descriptions of the destruction around their state, stories of neighbours and friends whose livelihoods vanished in a day.

“Two of my wife’s friends live in Asheville. One was devastated by Hurricane Katrina, lost everything. So she moved to Asheville,” said resident Dennis Spring.

“Looks like she’s wiped out again. … She has no drinking water. No gasoline. The food in her fridge has rotted.”

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

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

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.

President Joe Biden is expected to visit North Carolina 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 on Wednesday to tour the storm damage there, cancelling a previously scheduled campaign appearance in Pennsylvania.