More than 4,000 New York City workers were mobilized to work through the night and Wednesday to clear snow from 6,200 miles of streets, an effort hampered by frigid temperatures and traffic jams when the storm reached full force Tuesday, officials said.

Mayor Bill de Blasio urged people to avoid driving during Wednesday morning's rush hour. Plowing will not be finished, and "they're going to see white streets," said Sanitation Commissioner John Doherty.

Late Tuesday afternoon, Gov. Andrew M. Cuomo declared a state of emergency in which subway, railroad and bus service can be suspended or curtailed if snowfall accumulation reaches at least 10 inches. New York City Transit planned during the night to suspend express subway service so express tracks could be used to store trains usually kept in outdoor yards.

Crews from the city's sanitation department, working in 12- and 13-hour shifts of 2,000 workers each, fanned out in 1,700 vehicles and more than 450 salt spreaders. But salting was becoming ineffective with temperatures forecast to dip into the single digits overnight, officials said.

Doherty said salting crews would then switch to full-time plowing. "People have to adjust to the conditions," he said. Snow-clearing efforts were slowed by snarled streets during the evening rush, he said.

Police Commissioner William Bratton, responding to complaints of not enough traffic agents, said he pulled many of them out of intersections because "slipping and sliding" vehicles made it too dangerous for them.

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De Blasio said that vehicles from the city's parks and transportation departments would supplement sanitation's nighttime plowing efforts.

The mayor appealed to New Yorkers to stay inside during the worst of the storm and keep off the roads to give the plows a clear path.

"Avoid driving your own car. Take mass transit if you need to get somewhere," de Blasio said in a 6:45 p.m. briefing at the Office of Emergency Management in Brooklyn. Snowfall totals were already 3 to 7 inches, and 10 to 14 inches were forecast, he said.

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Officials were keeping an eye on conditions before deciding whether to cancel classes inthe city's public schools Wednesday.Alternate-side-of-the-street parking rules and trash and recycling collections were suspended through at least Wednesday.

De Blasio urged New Yorkers to check on elderly and vulnerable neighbors and to report the locations of homeless people on the street to the city's 311 hotline so they could be urged to accept free shelter.

With Emily Ngo