Two weeks of winter storms in the United States have turned roads into icy death traps, frozen people to death and caused power outages that could take weeks to fix.

The rain, snow, wind and bitterly cold temperatures have been blamed for at least 55 deaths.

Schools and roads have closed, and air traffic has been snarled.

Heavier-than-forecast snow fell in the eastern cities of New York, Baltimore and Washington, DC on Friday.

Michigan City in the state of Indiana received 43 centimetres of "lake-effect snow", a phenomenon in which cold air moves across the open waters of the Great Lakes and forms a snow-producing band.

But the biggest problems remained in places hit hard by storms earlier in the week.

On the west coast, the governor of Oregon declared a statewide emergency on Thursday night, nearly a week after the start of a crippling ice storm.

Thousands there have been without power since last weekend because of the freezing rain.

"We lost power on Saturday and we were told yesterday that it would be over two weeks before it's back on," said Jamie Kenworthy, who lives in Jasper, about 200 kilometres south of Portland, Oregon's largest city.

About 90,000 customers in the state remained without electricity Friday afternoon after back-to-back storms, according to poweroutage.us, a website that records power outages across the country.

Portland Public Schools cancelled classes for a fourth straight day amid concerns about icy roads and water damage to buildings. State offices in the city were also ordered closed.

Ice was also a problem in the nation's south.

Snow and freezing rain added another coat of ice in the southern state of Tennessee on Thursday.

More than 22.8cm of snow fell around Nashville in less than a week — nearly twice the yearly average.

Authorities blamed at least 17 deaths in Tennessee on the weather. Several of the deaths involved traffic wrecks.

In Washington County, a patient in an ambulance and a person in a pick-up truck were killed in a head-on crash when the truck lost control on a snowy road.

Americans have also died from exposure to the cold.

A 25-year-old man was found dead in a mobile home in the town of Lewisburg, about 90km south of state capital Nashville, after a space heater fell over and turned off.

In Kentucky, Governor Andy Beshear reported five deaths. The cold in Washington state was blamed for another five.

The people — most of them presumed homeless — died from exposure to cold in just four days last week in Seattle as temperatures plummeted to well below freezing, the state's medical examiner's office said.

Two people died from exposure as far south as the state of Louisiana, where temperatures in part of the state stayed below freezing for more than two days.

The cold broke so many water mains in Memphis, Tennessee, that the entire city was told to boil water.

In Jackson, Mississippi, law enforcement agencies were investigating whether social media rumours about a potential water outage during the cold snap prompted people to fill bathtubs with tap water.

The water system in Mississippi's capital experienced a drop in pressure that temporarily made thousands of customers' taps run dry on Wednesday and Thursday.

A significant drop in blood donations led the Tennessee-based Blood Assurance to recommend that more than 70 hospitals in five states halt elective surgeries until Wednesday to let the organisation rebuild its inventory.

The organisation cited the weather and several massive blood transfusions in the previous 24 hours in its plea to the hospitals in the southern states of Alabama, Georgia, Kentucky, North Carolina and Tennessee.

Aaron Robison, 62, who had been staying at one of Nashville's warming centres, said the cold would not have bothered him when he was younger.

But now with arthritis in his hip and having to rely on two canes, he said he needed to get out of the cold.

"Thank God for people helping people on the streets," he said. "That's a blessing."

On Friday, more bitterly cold air was spilling into the American Midwest from Canada. Forecasters warned wind chills dipping to -34C could be common through the weekend.

Since extreme cold weather set in last week, more than 60 oil spills and other environmental incidents have been reported in oil fields in the state of North Dakota.

Wind chills as low as -56.6C have strained workers and equipment and increased the likelihood of accidents.

The extreme weather is set to ease next week, with the forecast calling for above-average temperatures across most of the country, according to the US National Weather Service.