Bitter temperatures flirted with record lows on Sunday as "life-threatening" conditions put millions across the country in a deep freeze for Valentine's Day.
More than 38 million people from the Plains into the Midwest and East Coast were under winter-storm warnings or advisories overnight, according to The Weather Channel.
The coldest air mass of the winter brought the thermometer down to minus 6 degrees overnight in Minneapolis, while New Yorkers were urged to take "extreme precautions" against wind chill.
"These temperatures can be life threatening — especially for seniors, infants and people with medical conditions," New York City Mayor Bill de Blasio warned.
Forecasters warned Sunday morning will likely to be the coldest for many — with New England feeling the deepest chill.
"Stay indoors if you can," Weather Channel lead meteorologist Michael Palmer said. "With these type of temperatures you can get frostbite within a matter of minutes."
He said parts of New England will see "bitterly cold" wind-chill factors of 40 below zero, with air-surface temperatures also below zero for much of the Northeast.
New York City could get wind-chill factor of 20 below zero while upstate New York could experience wind chill of 50 below zero, he said.
Several cities had already set record lows as of 4:45 a.m. ET: Boston and Providence both hit minus 9, while Hartford hit minus 10 and Worcester, Massachusetts hit minus 15, according to the National Weather Service.
In New York, Central Park's reading of minus one broke a record there, too.
The National Weather Service issued a wind chill warning for the entire state of Connecticut for Saturday night into Sunday morning.
Air temperatures there are expected to tumble into the double-digits below zero in the hills and wind chills are expected to remain near 30 below zero, according to NBC Connecticut.
Police in Hartford canvassed the city overnight to offer shelter to the homeless.
"No one should be left out in the cold. These are bitter, nasty conditions," Lt. Gabriel Laureano told NBC Connecticut.
The Philadelphia area also was bracing for record-setting cold, with a low of 2 degrees expected and a wind-chill advisory in effect for the area outside the Poconos. Trenton's forecast low of 0 degrees would break a record set in 1916 while the expected minus 12 in the Poconos would break a 1970 record,according to NBC Philadelphia.
Further south, nearly the entire metro-D.C. area was under wind-chill advisories, according to NBC Washington. It reported that winds were expected to drive "feels like" temperatures to near or below zero.
Temperatures could warm up "a bit" on Sunday afternoon thanks to a separate storm moving up through the southern part of the U.S., the Weather Channel's Palmer said.
That storm system will shove the arctic air out but also bring a band of snowfall up through Washington, New York and Boston later Monday and into Monday night, Palmer added.
This post first appeared on NBCNews.com.