After Hurricane Sandy had done its worst, more than 8 million residents along the East Coast and other affected states were without power, according to the U.S. Dept. of Energy’s Office of Electricity Delivery and Energy Reliability.

For the hardest-hit states—New York and New Jersey, it was one of the worst hurricanes on record, darkening the New York City skyline and causing substations to shut down from surging water or storm-induced fire.

Utilities along the Eastern seaboard report that they are conducting damage assessments but have already restored power for many. They say they have brought in thousands of extra workers from across the country to help with the restoration effort.

In New York, where more than 2 million were without power by the time the storm had passed, Con Edison has said that it might be three days to a week before power is fully restored.

Alfonso Quiroz, spokesperson for Con Edison, says the damage to the utility’s stations and overhead wires was “extensive.” He says that it will take about three days to restore power to those with underground service, and “at least a week” for those with overhead electrical wires, which were ravaged by the storm’s high winds on Staten Island and West Chester County.

Complicating the restoration effort is damage to substations owned by Con Edison in New York and Public Service Electric and Gas (PSEG) in New Jersey. An explosion rocked through Con Edison’s East River station in Manhattan Monday night, an event that was captured on a video that went quickly viral.

Quiroz says crews are currently pumping out water from the underground stations and then will assess damage to the equipment. “After it’s assessed, we try to dry it out and then test it to see if it’s safe to restore,” he says.

Quiroz adds that about 807,000 customers in New York are without power. “We’ve restored some, but we’ve got a long way to go,” he says.

In New Jersey, where more than 2 million experienced power outages, the walls of water created by the storm surge flooded several substations along the Passaic, Raritan and Hudson rivers, disrupting service in Hudson, Essex and Middlesex counties.

PSEG says it will have to wait for the floodwaters to recede before it can assess the damage, dry out the equipment, replace equipment when necessary and re-energize the system to restore service. On its website, PSEG says, “It will be a slow, painstaking process.”

However, the utility says as of mid-day Oct. 31, it has restored service to 30% of the initial 1.5 million customers that lost power on Oct. 28-29.

PSE&G said flooded substations were restored that allowed power to return to Newark and Elizabeth and to Newark Airport. “Work continues on other stations including ones that serve Jersey City and Sewaren near Carteret,” the utility said.

Rachael Lighty, a spokesperson for Baltimore Gas & Electric, which provides power to more than 1.2 million electric customers in central Maryland, said on Oct. 30, “We’re still very much in the damage assessment portion of restoration.” She said the assessment would take between 24 and 48 hours, and that the restoration of power to all residents would be a “multi-day” process.

However, out of 340,000 total outages in the BG&E service area as a result of the storm, 187,771 had already had their power restored, she said.

PEPCO said on Oct. 31 that 95% of the power outages in the D.C. metro area had been restored. At the height of the storm, about 44,000 customers experienced outages.