NEW YORK/WASHINGTON (Reuters) - Major US East Coast cities struggled on Monday (Jan 25) to return to normal following a massive weekend blizzard that dropped about 61cm of snow on cities including New York and Washington.

Commuters faced delayed trains and buses and traffic was heavy heading into major metropolitan areas as many roads remained clogged with drifts of snow.

In Washington, the US Office of Personnel Management said federal government offices were shut on Monday, while further north, the New York Stock Exchange and the city's public schools were scheduled to open as usual.

At least 20 people have died from storm-related causes including traffic accidents and heart attacks while shovelling, with deaths reported in states stretching from Arkansas to New York.

Air travel remained seriously affected as some 1,390 US flights were cancelled on Monday, with Newark Liberty International Airport, New York's LaGuardia Airport and Washington Dulles International Airport the hardest hit, according to FlightAware.com.

More than 12,000 US flights were slashed from Friday through Monday, with some airlines cancelling flights into Tuesday, FlightAware reported.

The blizzard was the second biggest snowstorm in New York City history, with 68cm measured in Central Park by midnight on Saturday, shy of the record 68.3cm set in 2006, the National Weather Service said.

The NWS said 57cm fell in Washington at the National Zoo, and Baltimore-Washington International Airport notched a record 74.2 cm. The deepest regional total was 106.7cm at Glengarry, West Virginia.

In the Washington suburb of Arlington, Virginia, on Monday the main thoroughfare leading into Washington was clear but virtually empty as secondary roads were clogged by slush and partly blocked by huge mounds of snow created by plowing.

Dozens waited for more than half an hour for the subway into downtown as limited metro service began.

"It's beautiful to watch but impossible to get through,"said John Salmons, a 24-year-old designer who works at an architecture firm. "The main roads were fine it was just the secondary roads that were worst."

Even with federal government offices officially closed, the Supreme Court was open for business, scheduled to issue rulings and act on pending appeals from the snowbound courthouse across from the US Capitol building.

In past storms, including hurricanes and blizzards, the court also remained open, even hearing oral arguments.