A colossal winter storm has caused extensive damage and disruption in the United States, and its impact isn’t over yet.

It barrelled across an unusually large swathe of the country, dumping snow and ice from Oklahoma to the Deep South to New England.

The giant system knocked out power to more than a million customers, caused deaths in multiple states, prompted widespread school cancellations, ground travel to a halt and promised more uncertainty during the frigid days to come.

“This situation is expected to get worse before it gets better,” warned Mississippi Governor Tate Reeves (Republican), who implored residents to stay off perilous roads and detailed how some utilities had suffered “catastrophic damage” that could lead to prolonged outages.

Many areas across the US East Coast had received 15 to 30cm of snow and sleet today, as more powder and destructive amounts of ice were expected to continue to accumulate into tomorrow.

The map of misery was vast and varied, even as the storm’s impacts were far from over.

Power outages

With ice weighing down trees and electrical lines throughout the South, power outages rose rapidly in places such as Tennessee, where more than 300,000 remained without power, according to poweroutage.us.

More than 100,000 customers were without power each in Mississippi and Louisiana.

Flights cancelled

More than 11,000 flights were cancelled today, along with at least 2400 tomorrow.

Deaths

The Washington Post confirmed that at least six fatalities had been attributed to the storm.

Two men died in Louisiana and one in Austin because of hypothermia, and three people who appeared to be homeless were found outdoors in New York, local officials said.

Public health risks remained for millions of Americans, as precipitation continued to accumulate, electricity failures mounted and the mercury continued to fall in many places.

Extended cold

Far-reaching and fearsome cold was forecast to remain well after the snow and ice stopped falling. About 110 million people across the US can expect to experience subzero temperatures to Saturday.

Public warnings

State, local and federal officials implored people to exercise caution and common sense. They warned about the dangers of using generators indoors, the heightened potential for heart attacks while shovelling snow, the signs of hypothermia and the many risks of trying to drive on slick roads.

Vulnerable lines

Homeland Security Secretary Kristi Noem, who called the storm one of the most sprawling and impactful winter events in “possibly decades”, said on Fox News that its true toll remained unclear.

“This ice that has fallen will keep those lines heavy. Even if they haven’t gone down immediately, for several days we’re going to have the low freezing temperatures that will make sure that if we get a little bit of wind or we get some stress on those lines, they still continue to, could potentially, lose power, so we’re going to continue to monitor that,” Noem said.

She added that the Federal Emergency Management Agency is co-ordinating to make sure states have the equipment they need even after the storm has passed.

Children use sleds at the US Capitol in Washington DC. Photo / Tom Brenner, for The Washington Post

The East Coast

The Washington, DC, area saw less snow than some forecasts had anticipated. But a blanket of 7.5 to 18cm in most areas was topped with 5 to 10cm of sleet, creating significant disruptions.

All flights - more than 800 - were cancelled at Reagan National Airport, said Crystal Nosal, a spokeswoman for the Metropolitan Washington Airports Authority. Washington Dulles International Airport had more than 400 cancellations, and Baltimore-Washington International Marshall Airport had more than 400 flight cancellations, according to FlightAware, a flight-tracking website.

The storm also forced the detour or suspension of more than 100 Metro bus routes, according to the Washington Metropolitan Area Transit Authority, along with the cancellation of some Amtrak trains on the Northeast Corridor.

At the Capitol, where sledding had once been banned, a crowd of children once again took advantage of the fresh snow on the west front lawn.

More than 500 people in the District had signed up to be “snow heroes” to help shovel snow for elderly or disabled residents, according to the mayor’s office.

“It’s been years since I’ve seen this much snow here,” said Monica Reyes, 42, as she cleared off her car with a snow brush in Astoria, Queens. “I don’t even remember the last time we had a storm like this.”

Even amid the beauty of still-falling snow, the worries about how to navigate the days ahead loomed large.

Reyes, who works at a dental clinic, said she was fortunate that her office decided to remain closed. But she already was dreading her commute tomorrow, when she was expected to report to work in suburban Westchester County.

“Hopefully, I can make it to work, and hopefully it’s not going to be that messy,” Reyes said.

Some parents were having to think ahead about how to juggle work and snow days.

Ksenia Johnson, 34, an administrator at a hedge fund, wondered whether she would need to take tomorrow off to look after her two young children. “It’s amazing - it’s beautiful and it’s nature,” Johnson said of the blizzard, adding that she had relished past big snowstorms that swept through New York. “But it hits different when you have kids.”

Pittsburgh recorded more snowfall than in any other day in more than 15 years. Today’s snow total reached 23.8cm, according to the National Weather Service, the most since February 6, 2010, when 24.6cm fell during the second day of ‘Snowmageddon’.

The heaviest snow to come was expected to fall in a zone from St Louis to Pittsburgh and from New York to Boston, creating dangerous travel conditions along Interstates 70, 80 and 95.

Across this stretch, forecasters predicted more than 30cm of snow. By tomorrow the largest accumulations were expected to be found in a zone including parts of Pennsylvania, New York, Connecticut, Massachusetts, Rhode Island, New Hampshire and Vermont.

- Ruby Mellen, Kyle Rempfer, Liam Scott, Meagan Flynn, Ian Livingston and Mariana Alfaro contributed to this report.