WASHINGTON (REUTERS) - A fast-moving winter storm forecast to dump as much as 30cm of snow on the north-eastern United States (US) on Tuesday was expected to disrupt the evening commute for millions of people along the densely populated coast.

The storm prompted officials to close schools and many federal government offices in Washington, where about 2.5cm of snow had fallen by early afternoon.

"We are still expecting pretty major impacts on travel for the afternoon rush hour for both Baltimore and Washington," said Mr Carl Barnes, a meteorologist with the National Weather Service.

Winter storm warnings and advisories were in place from the central Appalachian Mountains north to southern New England, the National Weather Service said. The area includes all of the Middle Atlantic states and the busy I-95 highway corridor from Washington to Boston.

The polar front is expected to drive temperatures in the eastern half of the US to from 6 to 14 degrees Celsius below average. Southern New England could get up to 30cm of snow as the cold front picks up moisture from the Atlantic Ocean, the weather service said.

Hundreds of thousands of federal workers in Washington were ordered to stay home ahead of what was forecast to be the heaviest snowfall in three years. City schools and offices also shut down, and the White House called off its Tuesday press briefing.

But the Supreme Court remained open to hear cases, and organisers of the annual anti-abortion March for Life said Wednesday's rally would go on regardless of weather.

In Washington, more than 200 plows were deployed and transit worker Marcus Johnson readied for a long day clearing snow as he scattered salt outside a Metro subway station entrance.

"Sometimes snow is coming down so fast... it feels like a losing battle," said Mr Johnson, 24.

State governments in Delaware and Maryland shut down and Connecticut sent nonessential state workers home beginning at 3pm (4am Singapore time). The Maryland Transit Administration cut back rail and bus services.

Connecticut Governor Dannel Malloy and Virginia Governor Terry McAuliffe warned residents not to travel if they did not have to. Mr Malloy encouraged private-sector companies to consider releasing workers early.

The inauguration party for New Jersey Governor Chris Christie on Ellis Island in New York Harbor was cancelled because of the looming storm.

Some schools in North Carolina closed early, and public schools and colleges were shut across Virginia. Connecticut closed all its schools for Wednesday, and Hartford, the state capital, was sending students home early on Tuesday.

FLIGHTS CANCELLED

About 2,900 flights in the US had been cancelled on Tuesday, according to FlightAware.com, a tracking service.

The worst-affected airports were Philadelphia International and New York's LaGuardia.

Forecaster AccuWeather said the cold front would drop temperatures below freezing as far south as northern Florida.

The entire state of Minnesota was below -18 degrees Celsius early on Tuesday.

While the polar front grips the eastern US, the western half will see above average temperatures as a drought worsens, the Weather Service said.

The polar air is something of a repeat of the cold snap that gripped much of the US at the start of the year. Cold and snow snarled air and road travel, shattered temperature records and contributed to at least nine deaths.