Workers shovel snow during a snowstorm at Times Square in the Manhattan borough of New York January 23, 2016. [Photo/Agencies]

NEW YORK/WASHINGTON - A monster blizzard that has paralyzed much of the US East Coast intensified on Saturday as it barreled into New York City, forcing the closure of all bridges and tunnels into the largest US city and prompting a travel ban on area highways.

At least 13 people have been killed in weather-related car crashes in Arkansas, North Carolina, Kentucky, Ohio, Tennessee and Virginia, and a 14th person died of a heart attack while shoveling snow in Maryland.

After dumping nearly two feet (60 cm) of snow on the Washington, D.C., area overnight, the storm unexpectedly gathered strength as it spun northward and headed into the New York metropolitan area, home to about 20 million people.

By Saturday afternoon, forecasters had bumped their snowfall predictions to up to 30 inches (76 cm) in New York and New Jersey, and snowfall was picking up again in the nation's capital after a midafternoon lull.

The National Weather Service (NWS) said 20 to 25 inches was most likely in New York, but would not rule out higher accumulations.

As a consequence, New York Governor Andrew Cuomo declared a state of emergency as 10 other state governors have done. He also announced a ban on all travel on New York City area roads, as well as Long Island, except for emergency vehicles, as of 2:30 p.m. EST (1930 GMT). All bridges and tunnels into the city from New Jersey will also close, he said.

Subways running above ground and trains operated by the Long Island Rail Road and Metro-North will halt service at 4 p.m. EST because snow falling at a rate of 3 inches per hour proved too much for plows on roads and railways, Cuomo said.

The impact of the travel ban on the New York's thriving financial services industry is likely to be minimal over the weekend, and it was too soon to tell how much the heavy snow will affect Wall Street when it is due to reopen on Monday.

On Broadway, however, the impact was immediate. Theaters canceled Saturday matinee and evening performances at the urging of New York City Mayor Bill de Blasio, who warned that the storm may rank among the top five blizzards ever to hit the largest US city.