Continuity mistake: In the same shot, note the top of the twin towers are in the clouds - its not a real nice day in NYC. But later when they're on the dock, there's not a cloud to be seen.
Continuity mistake: When the love interest (I forget her name) finally gets out of the tunnel by the blow-out thing, the water on the surface is all churned up, choppy, etc. Cut to a helicopter shot, where the water is a flat as a millpond.
Continuity mistake: When Kit gets all the survivors onto the top of the cars, out of the water to keep them "high and dry", Ashley's parents are standing on top of a car next to each other. In one particular shot there's a large distance between them, but in the previous shot they're next to each other. (00:55:50)
Continuity mistake: When the security guard is trapped underneath the truck, in daylight the amount of water he is drowning in changes. From the front angle he is also most covered in water and from the side angle he has more time.
Continuity mistake: When the black criminal dies from an injury caused by the huge explosion at the mid river passage, Kit is leaning against the front bumper of a burnt out car, but a few shots later when the camera cuts to a wider angle, the car has vanished and all we see is the old man, Kit and the criminal on the floor with no car, but in the following shot the car reappears again. This has nothing to do with camera angles. (00:51:20 - 00:52:05)
Continuity mistake: When we see Madelyne for the first time, she is in her apartment and gets a drink. She then goes to sit down next to her computer, she switches on her lamp and puts something down on the table. In the following shot it looks like she reaches for something with her right arm over her computer, but this was not seen in the previous shot. (00:05:10)
Continuity mistake: When Nord is in the mid river passage on the cellphone, and it cuts to a large object, the large object is sitting on something, which is seen, but when one of its chains breaks loose from the wall, nothing is holding it at the bottom when it begins to swing. (00:47:10)
Factual error: In the beginning of the movie, the explosion in the Holland Tunnel is caused when a car crashes into the trucks carrying toxic waste barrels. In real life, it is against the law for vehicles carrying hazardous chemicals to use any of the tunnels. Even if the drivers didn't know this, which is highly unlikely, they would have been pulled over by the Port Authority cops as soon as they headed for the entrance - lots of yellow barrels would be a bit suspicious.