A giant winter “bomb cyclone” walloped the United States (US) East Coast on Friday with heavy snow and freezing cold that made for treacherous travel conditions and bone-chilling misery.

Four people were reported killed in the southeastern states of North and South Carolina, where icy roads sent vehicles skittering.

The National Weather Service said early on Friday that very cold temperatures and wind chills will follow for much of the eastern third of the US through the weekend.

A cold wave gripping a large section of the US had already been blamed for a dozen deaths.

Thousands of flights were cancelled and schools closed in many localities as snow piled up and blizzard conditions began taking hold in the northeast.

Officials closed the runways at La Guardia and Kennedy Airports in New York.

Temperatures were so low in northern New York that Niagara Falls, the giant waterfalls straddling the US-Canadian border, froze.

Snowfall eased by nightfall but temperatures were set to plunge to minus 13 Celsius and remain sub-freezing all weekend.

Weather forecasters dubbed the event a “bomb cyclone,” their nickname for a phenomenon known as “bombogenesis,” in which a weather system experiences a sharp drop in atmospheric pressure and intensifies rapidly, unleashing hurricane-force winds.

Americans along the East Coast faced potential power outages in bitterly cold sub-freezing temperatures.

About 30,000 customers in Virginia and North Carolina were deprived of electricity, according to CNN.

Some 3,000 customers were hit in New York and about 10,000 in Boston, although service was partly restored at the end of the day.

In coastal Boston, the storm was accompanied by giant waves that led to what Massachusetts Governor Charlie Baker described as “historic flooding” that inundated the city’s eastern streets as well as coastal areas of the state.