The driver was taken to Jersey City Medical Center with critical injuries, they said.
A passenger in the truck sustained a broken femur, police at the scene told Daily Voice.
The driver -- who apparently suffered a heart attack -- and another person who was on the street above were also hospitalized, as were several people who were aboard a bus that struck the truck after it landed, they said.
In total, a dozen people were injured, the Hudson County Prosecutor's Office tweeted.
Most of the injured were taken to the medical center, while others went to Hoboken University Medical Center and Hackensack Meridian Health Palisades Medical Center, according to the tweet.
Route 495 was closed in both directions for nearly six hours and was reopened around 7 p.m. Wednesday, on one of the busiest traffic days of the year.
All bus service from the Port Authority's midtown terminal was temporarily suspended until 4:30 p.m.
Three and a half hours earlier, the truck came barreling down 30th Street, witnesses said.
It struck an SUV and minivan outside the Union City post office and headed straight for the Palisade Avenue overpass, damaging a planter and toppling a pole.
The truck then crashed through a fence and sailed off the overpass.
The cab struck the blacktop nose first and flipped, landing upside-down on the north side embankment of the highway leading from the Lincoln Tunnel toward the New Jersey Turnpike and Route 3.
DAILY VOICE photo
The Hudson County Regional Collision Investigation Unit was investigating, assisted by local law enforcement.
PHOTOS: Sheri Marshall-Nicosia for Daily Voice
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PHOTO: Courtesy Douglas Villalta
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