As we mentioned, downed power lines could keep millions of americans in the dark long after the storm has passed. Already, an army of pow er company workers are on their way, from as far away as ohio... See More
As we mentioned, downed power lines could keep millions of americans in the dark long after the storm has passed. Already, an army of pow er company workers are on their way, from as far away as ohio and oklahoma. David kerley is in delaware tonight. David? Reporter: Good evening, david. You are right. There is an army headed here, an army of utility workers. If the predictions are right, these lights are going to be out, and those workers are going to be extremely busy. The power was going out even before the full force of sandy hit shore. See the fuse? Reporter: Larry jackson knows the worst is still to come. Probably be working 16-hour days. Reporter: Thousands of utility workers are in their trucks and headed east tonight, to repair what are expected to be massive power outages. These beach vacationers packed up to head home, inland. Actually, the aftermath is what we're concerned about. Reporter: No power. Right. And for days. Reporter: The power outages are expected to be widespread. It may take a long time not only to clear, but also to get, for example, the power companies back in. Reporter: During hurricane irene last year, about 6 million homes lost electricity. This researcher plugged in all the information into a new program and he believes this will be worse. Our estimate at this point is 10 million. It could be higher. Could be lower. Reporter:10 million or more without power for a week to ten days. Which is why this wisconsin company has added extra shifts, trying to build as many portable generators as quickly as possible. Officials worry that residents might misuse some of those generators, putting them indoors or stringing extension cords dangerously. Many seem to be heeding the warnings, checking off their lists of preparedness. Batteries, water, nonperishable food. I'm nervous about losing power. I'm nervous about the storm. Reporter: Of course, the real worry here are trees that bring down these power lines. We all know not to touch the power line, but the experts say leave the limbs alone, too. Call the power company, let them handing the entire thing. Looks like it could be really a mess later this week. David kerley, our thanks to you tonight.
This transcript has been automatically generated and may not be 100% accurate.