The major American stock exchanges closed for the day, the first unplanned shutdown since the Sept. 11 attacks in 2001. The floor of the NYSE, typically bustling with traders on a Monday morning, fell within the city's mandatory evacuation zone. The United Nations canceled all meetings at its New York headquarters.
New York called off school for the city's 1.1 million students, and the more than 5 million people who depend on its transit network every day were left without a way to get around. Most planned to stay inside anyway.
"If you don't evacuate, you are not only endangering your life, you are also endangering the lives of the first responders who are going in to rescue you," Mayor Michael Bloomberg warned. "This is a serious and dangerous storm."
New Jersey Gov. Chris Christie was typically blunt: "Don't be stupid. Get out."
The storm bore down barely a week before the presidential election. Wary of being seen as putting political pursuits ahead of public safety, Obama and Republican nominee Mitt Romney reshuffled their campaign plans.
In Virginia, one of the most competitive states, election officials eased absentee voting requirements for those affected by the storm. Three other closely contested states, New Hampshire, North Carolina and Ohio, were within Sandy's reach. Early voting was canceled Monday in Maryland and Washington, D.C., both reliably Democratic.
After hooking inland, Sandy was expected to collide with a wintry storm moving in from the west and cold air streaming down from the Arctic. Forecasters said the combination could bring close to a foot of rain in places, a potentially lethal storm surge of 4 to 11 feet across much of the region, and punishing winds that could cause widespread power outages that last for days.
Craig Fugate, chief of the Federal Emergency Management Agency, said FEMA teams were deployed from North Carolina to Maine and as far inland as West Virginia, bringing generators and basic supplies that will be needed in the storm's aftermath.