ATLANTIC CITY, N.J., Oct. 31 (UPI) -- Parts of the United States still felt megastorm Sandy's effects, which brought death and destruction to a dozen states, as it moved toward Canada Wednesday.

Sandy, now a surface trough of low pressure, has been blamed for more than 40 deaths in the United States, including 22 in New York City, officials said.

The National Weather Service's Hydrometeorological Prediction Center said in its 5 a.m. EDT advisory there was no discernible surface circulation for what remained of Sandy.

At least 8 million customers were without power Wednesday, and more than 18,000 flights had been canceled since Sandy first started moving along the East Coast. Sandy also was responsible for at least 67 deaths in the Caribbean.

President Obama signed federal emergency declarations for 10 states and the District of Columbia and spoke with 20 governors and mayors on a conference call. He scheduled a tour Wednesday of New Jersey to survey some of the damage with Gov. Chris Christie.

New York City financial markets were to resume trading Wednesday even though much of the city was without electricity.

At least 80 homes caught fire and burned in a Queens neighborhood.

New York's subway system suffered the most devastating damage from floodwaters in the system's 108-year history, Metropolitan Transportation Authority Chairman Joseph Lhota said Tuesday. The New York Harbor saltwater that gushed into subway tunnels may have corroded signal and switching systems, he said.

He said service would not be restored for at least four or five days.

New York buses began running again Tuesday afternoon and Mayor Michael Bloomberg ordered a ride-sharing program for taxis.

New York, New Jersey and Connecticut reopened many closed roads and bridges.

In New Jersey, much of Atlantic City's famed Boardwalk was destroyed and the resort city for gambling and conventions was all but submerged.

New York police executed several daring air rescues, dropping lifelines to rescue at least six people, including a child, The New York Times reported.

Police said there haven't been any signs of looting or other indications of crimes of opportunity taking place because of the storm, the Times said.

During an evening news conference Tuesday, Bloomberg said more police would be part of overnight shifts in the parts of the city still in darkness.

"This is the calm after the storm," one police officer told the Times.

The Port Authority of New York and New Jersey said Tuesday night Newark and Kennedy airports would reopen Wednesday with limited service, but New York's LaGuardia Airport, where runways remained flooded, would stay closed.

Stewart International Airport, 60 miles north of the city, would also reopen with limited service, the Port Authority said.

Damage from the storm throughout the Northeast could be as much as $20 billion, catastrophe-risk modeling firm EQECAT said.

Gale warnings and small craft advisories were in effect for parts of the Great Lakes, and small craft advisories were posted for much of the East Coast, the Hydrometeorological Prediction Center said.

Winter storm warnings and advisories were posted for the mountainous regions of southwest Pennsylvania, western Maryland, West Virginia, eastern Tennessee, eastern Kentucky and extreme western North Carolina.

At least 2 feet of snow has fallen in parts of Maryland, West Virginia, Virginia and North Carolina. NWS said additional accumulations of 2-4 feet were expected in the mountains of West Virginia into far western Maryland and southwestern Pennsylvania.

Forecasters said high waters would subside along the East Coast Wednesday from North Carolina to Massachusetts, but flooding could still occur along the coast and along the Great Lakes.

Dangerous surf conditions were expected from Florida to New England for the next couple of days.