The National Weather Service declared a 24-hour blizzard warning for the Washington-Baltimore region until 2200 on Saturday (0300 GMT on Sunday).
Most flights from the Washington-Baltimore area's three main airports and Philadelphia International Airport have been cancelled.
Hundreds of car accidents were reported, including two fatalities - a father and son who died while helping another motorist in Virginia.
US national rail service Amtrak cancelled a number of trains between New York and Washington, and also between Washington and some southern destinations.
Local weather forecasters said the Washington area could see its heaviest snowfall in 90 years.
It comes less than two months after a December storm dumped more than 16in (41cm) of snow in Washington.
The usually traffic-heavy roads of the capital were deserted, while the city's famous sites and monuments were covered with snow.
DC traditionally panics when it comes to snow - this time, it may be more justifiable than most times.
Becky Shipp Resident of Arlington, Virginia
The Washington Metro was operating only on underground lines, and bus services were cancelled.
US government offices in the Washington area closed four hours early on Friday, while the Smithsonian museums and National Zoo were closed on Saturday.
Debi Adkins, who lives just outside the city of Baltimore, told the BBC: "The snow started at 1130 yesterday morning and it just hasn't stopped... about 20 inches came overnight - and thunder and lightning.
"I'm not going anywhere - I couldn't if I wanted to. You just can't get your cars out. The front door of the building I live in is closed shut, so I just can't get out."
Ushaa Shyam Krishna in Chantilly, Virginia, said he - like many others - had stocked up on essential food items ahead of the storm.
"For the first few hours after the storm began, my daughter and I tried to shovel the snow, but now we have given up," he said.
"On Thursday the supermarkets were half empty - we went again yesterday and the shelves were totally empty."
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