Most of those cancellations are tied to the approaching hurricane, now a Category 2 storm with winds expected onshore late Thursday at more than 80 miles per hour.
As Florence drew near, President Donald Trump tweeted that FEMA and first responders are "supplied and ready", and he disputed the official conclusion that almost 3,000 people died in Puerto Rico, claiming the figure was a Democratic plot to make him look bad.
"Once those high winds get here.it will be very hard, if not impossible, for anybody to come rescue you if you are in harm's way in one of those zones", McMaster said at a news conference Wednesday.
The result could be catastrophic inland flooding that could swamp homes, businesses, fields and industrial sites.
Water kills more people in hurricanes than wind does.
More than ten million people are under storm watches and warnings this morning.
He warned residents to be prepared for mass power outages that could last for days or weeks, echoing the sentiments shared by Duke Energy on Wednesday.
Typhoon pounds China after mud buries dozens in Philippines
In the neighbouring gambling enclave of Macau, all 42 casinos shut down for the first time in its history as the storm approached. Dozens of people have died and more are feared to be trapped by landslides, especially in the Cordillera mountain region.
"It's going to coming roaring up to the coast Thursday night and say 'I'm not sure I really want to do this and I'll just take a tour of the coast and decide where I want to go inland, '" said Jeff Masters, meteorology director of the private Weather Underground. Airlines canceled almost 1,000 flights and counting.
FlightAware expects the number of cancellations to rise, although "the limited number of hubs being impacted by Florence will likely limit the scale of disruption that cascades through the national air travel system", spokeswoman Sara Orsi said in a statement. The shopping list for people who have made a decision to ride out the storm at home: plywood to board up their windows, sandbags, bilge pumps, generators, trash bags, potato chips, bottled water and wine. The two hardware chains said they sent in a total of around 1,100 trucks.
Florence is a large hurricane.
Storm surge warnings were issued from South Santee River in SC to Duck, North Carolina. The timing of the official landfall could change with any shift in Florence's track over the next 12-18 hours.
In addition to the storm surge, "There is going to be a lot of rain", North Carolina Gov. Roy Cooper said on Thursday.
Computer models of exactly what the storm might do varied, adding to the uncertainty.
Florence is moving toward the northwest near 10 miles per hour.
Trump, who famously DVRs, must have finally caught up with the controversy in which he said his response to Hurricane Maria was "tremendous". "If you're blowing 100 or 120 miles per hour on homes, they're going to start to deteriorate". Just because of the sheer size of it. Three other Southern raceways also opened campgrounds to evacuees. The trend is "exceptionally bad news", said University of Miami hurricane researcher Brian McNoldy, since it "smears a landfall out over hundreds of miles of coastline, most notably the storm surge".
Usually when a storm approaches the coast, forecasters can tell with ever-increasing accuracy who will get walloped.