New York City-area authorities on Thursday urged residents to stay home, ordered highways be shut down and scaled back some mass-transit service as a dangerous snowstorm barreled into the region from the Midwest.

One day into his new job, the city's mayor, Bill de Blasio, said the Department of Sanitation was ready for a nor'easter predicted to dump a half a foot or more of snow on the city. The storm was expected to be the first test of the de Blasio's administration, and the city had mobilized about 2,300 sanitation workers for each 12-hour shift, 450 salt spreaders and 1,700 trucks with plows.

"We are not taking anything lightly," Mr. de Blasio said, adding the city had "all hands on deck."

The National Weather Service predicted treacherous conditions, with wind gusts from 25 to 30 miles an hour and wind chills below zero. By late Thursday, weather service officials reported about two inches of snow, with wind gusts of 40 mph or more in New York City and Long Island. Temperatures were in the low 20s, with wind chill around 5 degrees. States of emergency were declared in New York and New Jersey.

"Exposed skin could start to freeze within 15 minutes," said Tim Morrin, a meteorologist at the National Weather Service.