In Philadelphia, officials said they would send extra outreach teams Monday night to urge homeless people into shelters. Shelter capacity was increased as a result of a "code blue" declaration.
A code blue, typically declared when temperatures and wind chills drop below freezing, also was in effect in Bucks and Montgomery Counties.
Philadelphia officials said they had 70 vehicles applying salt Monday night to primary and secondary roads to reduce ice.
Pets should have been brought indoors or otherwise protected against the cold, said Red Cross spokesman Dave Schrader.
The Philadelphia School District will be open Tuesday with no delays, officials said Monday night, though Edison High School will be closed for a second day because of water damage from a broken pipe.
Airline disruptions around the country caused flight delays and cancellations at Philadelphia International Airport, spokeswoman Victoria Lupica said. Travelers were advised to arrive early at the airport Tuesday in anticipation of long lines.
Amtrak announced that it would reduce its Tuesday schedule for the Acela Express and Northeast Regional between Washington and Boston because of the extreme cold.
Passengers with reservations were being accommodated by other trains or were being notified in advance, the railroad said. Power-line problems in Wilmington disrupted service between Philadelphia and Washington for several hours Monday night.
In New Jersey, officials were preparing for the freezing weather by opening warming centers, treating roads for ice, and reminding residents to warm their homes safely.
Many New Jersey counties, including Camden, Burlington, and Atlantic, issued code blue alerts for Monday night into Wednesday morning.
Every municipality must have a warming center for those without heat. Officials instructed those in need to dial the 211 nonemergency line or call local police for warming addresses.
"Most people take a code blue pretty seriously," said Rebecca Fuller, director of communications for Volunteers of America. "This is not just uncomfortable temperatures, it's life-threatening."
Fuller said workers started searching for people who live in tent encampments throughout Camden, to encourage them to seek indoor shelter.
At the Shore, the cold had brought 40 or 50 people to the Atlantic City Rescue Mission, which typically provides shelter for 250 homeless people.
"Now we are up over 300," said Debbie Giacomoni, the mission's community and government liaison, adding that sleeping mats had been placed in the dining room to accommodate the overflow. "We absolutely have seen more people."
With more people in need, Giacomoni said, resources are stressed. Those who want to donate clothes, toiletries, or other items can visit the mission's website, www.acrescuemission.org, for more information.
Steve Schapiro, a spokesman for the New Jersey Department of Transportation, said workers had been monitoring road conditions and treating areas where ice could form. He warned motorists to watch for black ice.
"Conditions can change quite quickly and people should be cautious," Schapiro said, saying turns and ramps can be particularly difficult. "There could be some icy patches, and that could change from mile to mile."
PSE&G, which provides electricity for 2.2 million customers and gas for 1.8 million, has modified pressure to keep gas customers properly supplied, said Karen Johnson, a PSE&G spokeswoman. She said no electrical shortages were anticipated.
Furnaces will be working hard through the cold weather, Johnson said, and homeowners may want to consider lowering their thermostats.
In Philadelphia, anyone seeking an outreach team for homeless people who are still outdoors can call 215-232-1984.
Inquirer staff writers Kristen A. Graham, Robert Moran, and Anthony R. Wood contributed to this article.