Western New York was hardest hit by an Arctic deep freeze and storm front that extended over most of the United States for days as far south as the Mexican border.
Across the country, at least 60 lives have been lost in weather-related incidents, NBC News said.
According to a count of the toll in the New York Times on Tuesday, more than 30 storm-related deaths have been reported in western New York's Erie and Niagara counties.
Some of those who died were found frozen in cars, others in snowbanks outside, and others from medical emergencies such as cardiac arrest while shoveling snow, said Erie County's chief executive Mark Poloncarz.
In New York state, authorities described ferocious conditions, particularly in Buffalo, with hours-long whiteouts, bodies being discovered in vehicles and under snow banks, and emergency personnel going "car to car" searching for survivors.
Buffalo - a city in Erie County, New York that is no stranger to foul winter weather - is the epicenter of the crisis, buried under staggering amounts of snow.
"Certainly it is the blizzard of the century," New York Governor Kathy Hochul told reporters, adding it was "way too early to say this is at its completion."
Hochul said some western New York towns got walloped with 0.75 to one meter of [new] snow overnight."
Hochul spoke on Monday with President Joe Biden, who offered "the full force of the federal government" to support New York state, and said he and First Lady Jill Biden were praying for those who lost loved ones in the storm, according to a White House statement.
Biden also approved an emergency declaration for the state, the White House said.
Speaking at a press conference earlier Monday, Poloncarz said Erie's death toll would likely surpass that of Buffalo's infamous blizzard of 1977, when nearly 30 people died.
With most of Buffalo "impassable," he joined Hochul in warning residents to hunker down and stay in place.
National Guard members and other teams have rescued hundreds of people from snow-covered cars and homes without electricity, but authorities have said more people remain trapped.
A driving ban for residents remained in effect for all of Buffalo. Poloncarz, speaking at a press briefing Tuesday, urged residents to stay home and the curious to stay away.
"Too many people are ignoring the ban," he said. "Please, please, please do not drive in the city. It's ugly right now."
He said people were driving into the city "who want to just look at the snow."
Erie County Sheriff John Garcia called the storm "the worst" he has ever seen, with periods of zero visibility and authorities unable to respond to emergency calls.
"It was gut-wrenching when you're getting calls where families are with their kids and they're saying they're freezing," he told CNN.
Hochul, a native of Buffalo, said she was stunned by what she saw during a reconnaissance tour of the city.
"It is (like) going to a war zone, and the vehicles along the sides of the roads are shocking," Hochul said, describing eight-foot (2.4-meter) drifts against homes as well as snowplows and rescue vehicles "buried" in snow.
The extreme weather sent temperatures to below freezing in all 48 contiguous US states over the weekend, including in Texas communities along the Mexico border where some newly arriving migrants have struggled to find shelter.
This article was compiled with data from Reuters and Agence France-Presse.