New York State Governor Andrew Cuomo imposed a ban on all local and state roads across the city of 8.4 million residents, Long Island and crossings west to New Jersey from 2:30 pm (1930 GMT).
Bus services were suspended at noon, and overland commuter and subway trains in and out of Manhattan were to be shut from 4:00 pm as Broadway cancelled performances, museums closed and shops shuttered.
Cuomo and New Jersey Governor Chris Christie banned travel on bridges and tunnels that connect Manhattan across the Hudson River, including the George Washington Bridge, ordinarily the busiest in the world.
Only authorized emergency vehicles, hazard vehicles and critical health care personnel are permitted to use the roads, officials said.
"Safety is our number one priority," Cuomo told reporters. "We are doing everything necessary to keep people safe, and I encourage all New Yorkers to wait out the storm indoors."
The vast majority of flights into and out of New York area airports -- La Guardia, John F. Kennedy and Newark -- were also cancelled.
Mayor Bill de Blasio warned that more than 20 inches (50 centimeters) of snow was expected to accumulate in the city and that the storm could prove unprecedented since records began in the 19th century.
"If it goes past 20 inches, it will be in the top five in terms of accumulation literally in our recorded history," he said. "This is a very big deal."
By early afternoon, Central Park had already recorded 14.7 inches of snowfall.
Public transit in Washington was shut down for the weekend as was most rail service in Philadelphia, as the monster storm -- dubbed "Snowzilla" -- dumped mounds of snow along the US East Coast.
Up to two feet (61 centimeters) was expected in several major cities.
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