NEW YORK, United States (AFP) — A massive winter storm was set to drop a hazardous mix of freezing rain and heavy snow on some 160 million Americans starting Friday, threatening “catastrophic” icy conditions.

Multiple US states had declared states of emergency as meteorologists said the storm system forming off the California coast would soon begin its march across much of the continental US, covering a wide swath of the country’s middle including the Rockies and Plains.

It could bring “catastrophic ice accumulation”, the National Weather Service said, and could result in “long-duration power outages, extensive tree damage, and extremely dangerous or impassable travel conditions”.

The storm was expected to linger for days, shifting into the heavily populated mid-Atlantic and northeastern states while crippling daily life and ushering in a frigid air mass across wide areas of the country.

More than 1,500 weekend flights had already been cancelled, according to the tracker Flightaware, including many in Texas.

State officials there vowed that the power grid that failed during a deadly winter storm five years ago and left millions without power was prepared this time around.

The southern state’s Republican Governor Greg Abbott told journalists Thursday that “there is no expectation whatsoever that there’s going to be any loss of power from the power grid”, which he said “has never been stronger, never been more prepared and is fully capable of handling this winter storm”.

Meanwhile, in New York, Democratic Governor Kathy Hochul warned of extreme cold that could make even short trips outdoors dangerous, urging people to stock up now, avoid unnecessary travel and stay inside.

She emphasised risks ranging from hypothermia and heart attacks while shovelling to power outages, while stressing precautions like protecting pipes, using heaters safely and checking on vulnerable neighbours.

Hochul told reporters the state is fully mobilised, with thousands of utility workers, ploughs, and emergency crews on standby to keep roads clear, restore power and protect those most at risk.

“Five or six minutes outside could literally be dangerous for your health,” she said, adding that “hypothermia can settle in quickly, frostbite can settle in”.

The storm is set to usher in frigid temperatures and dangerous winds that could last a week in some areas. As of Friday morning, parts of the Upper Midwest were already experiencing wind chills forecast to hit in the range of -55F (-48C).

The brutal storm system is the result of a stretched “polar vortex”, an Arctic region of cold, low-pressure air that normally forms a relatively compact, circular system but sometimes stretches into a more oval shape, sending cold air spilling across North America.

Scientists say the increasing frequency of such disruptions of the polar vortex may be linked to climate change, though the debate is not yet settled and natural variability also plays a role.

But President Donald Trump — who scoffs at climate change science and has rolled back green energy policies — wasted no time in questioning how the cold front fit into broader climate shifts.

“Record cold wave expected to hit 40 states. Rarely seen anything like it before. Could the environmental insurrectionists please explain — WHATEVER HAPPENED TO GLOBAL WARMING???” the Republican leader posted on his platform Truth Social.

State officials were more focused on the immediate threats the powerful storm posed to residents, with at least 14 states from the south to the northeast as well as Washington DC declaring states of emergency.

Political leaders across the country were encouraging people to stock up on food and dry goods, prepare emergency first aid and supply kits and keep their vehicle gas tanks full to prevent fuel lines from freezing.