Corey Ihasz (R) of Potomac, Maryland stands in line to pay for his new snow blower at the Lowe's store in Kentlands, Maryland January 21, 2016.[Photo/Agencies]

"Anyone who has the illusion you're going to be taking big trips over the weekend, get that out of your mind," de Blasio said at a news conference.

Speaking at a news conference surrounded by dump trucks being loaded with salt, Bowser said the US capital's public schools would be shut on Friday and local government offices would close at noon.

Bowser apologized for not having the city ready for about 2 inches (5 cm) of snow that snarled Wednesday's rush hour traffic, in what many Washington residents saw as a bad omen for the weekend.

Asked on Thursday how she thought Washington would cope with the blizzard, Patricia DeWolf, a 63-year-old retiree, said, "If last night was an indication, not very well." She spoke outside a Safeway grocery store, where she had been loading up on supplies.

The National Weather Service put Washington and Baltimore under blizzard warnings from 3 pm Eastern (2000 GMT) Friday through Sunday morning.

It forecast up to 2 feet (61 cm) of snow in the capital, and as much as 30 inches (75 cm) in western suburbs, with winds gusting to 50 miles per hour (80 kilometers per hour).

"Visibility will be reduced to near zero in whiteout conditions," it said.