Four people were reported killed in the southeastern states of North and South Carolina, where icy roads sent vehicles skittering.
A cold wave gripping a large section of the United States had already been blamed for a dozen earlier 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.
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 8 Fahrenheit (minus 13 Celsius) and remain sub-freezing all weekend.
'Very dangerous'
With up to a foot (30.5 centimeters) of snow expected in parts of New York, accompanied by powerful wind gusts, schools were closed. More than a foot of the white stuff was expected in Boston.
Governor Andrew Cuomo warned: "Frigid temperatures are expected overnight, which should further complicate the situation" adding there had been a number of serious accidents.
Wind gusts of up to 55 miles (88.5 kilometers) per hour were expected through Friday on Long Island and southeastern Connecticut, with wind chills as low as - 20 F (- 29 C), increasing the risk of frostbite and hypothermia from prolonged exposure.
The National Weather Service warned of "multiple hazards: moderate to heavy snow, low visibility, strong to damaging winds, coastal flooding, and hazardous seas," from the developing storm moving northward towards New England.
"Anticipate travel and economic impacts today and tonight with accumulating snow and white-out conditions. Expect downed trees and power lines resulting in scattered to widespread outages."
Bomb cyclone
The storm owes its moniker to a process known as bombogenesis, in which a weather system experiences a sharp drop in atmospheric pressure and intensifies rapidly, with blizzard-like conditions combined with hurricane-force winds.
About 12 deaths have already been blamed on the frigid temperatures this week.
Winter storm warnings were in effect from the Mid-Atlantic region northward through New England, meaning that hazardous conditions were imminent.
Virginia Governor Terry McAuliffe declared a state of emergency. "Virginians living in the impacted areas should stay off the roadways to allow local and state road crews and first responders to do their jobs safely and efficiently," he said.
"With continued frigid temperatures expected to last for several more days, road conditions will remain treacherous beyond the expected end of the snowfall today," he added.
National rail line Amtrak cancelled service between Washington and Newport News, Virginia.
In Washington, federal agencies opened two hours late and Senate Majority Leader Mitch McConnell announced the chamber would hold no further votes this week, shortening what was already a short workweek due to the New Year's holiday.
Senators had only returned to the upper chamber Wednesday, and they face a series of critical votes in the coming weeks, including on funding to prevent a government shutdown and spending cuts.
Workers clear the boardwalk during a winter snowstorm in Atlantic City, N.J., Thursday, January 4, 2018. Source: AAP
Travel disruptions
Airlines have scrapped more than 4,200 flights into and out of the United States so far due to the storm, and delayed 2,200 others, according to flight tracker FlightAware.
Nearly 75 percent of flights departing Boston and New Jersey's Newark airports were cancelled, though only about a quarter of flights to and from New York's main airport were scrapped.
Air France cancelled all flights Thursday and Friday from Paris to New York and Boston.
Virginia Governor Terry McAuliffe declared a state of emergency.
"Virginians living in the impacted areas should stay off the roadways to allow local and state road crews and first responders to do their jobs safely and efficiently," he said.
"With continued frigid temperatures expected to last for several more days, road conditions will remain treacherous beyond the expected end of the snowfall today," he added.
National rail line Amtrak cancelled service between Washington, D.C., and Newport News, on the Virginia coast.
In Washington, despite only a dusting of snow, federal agencies opened two hours late, many schools were closed and Senate Majority Leader Mitch McConnell announced the chamber would hold no further votes this week, curtailing what was already a short work week due to the New Year's holiday.
Senators had only returned to the upper chamber Wednesday, facing a series of critical votes in the coming weeks, including on funding to prevent a government shutdown and spending cuts.
