"This is a terrible tragedy ... people on their way home all of a sudden taken from us," New York Mayor, Michael Bloomberg, said on Wednesday from the scene of the accident on the Staten Island shoreline.
The precise cause of the crash was unclear.
Bloomberg confirmed 10 dead with 34 passengers taken to hospital, but added that the numbers could change given the seriousness of some of the injuries.
Local television stations, citing rescue sources, said 14 people had been killed.
Fire department officials said some passengers lost limbs in the crash, which occurred at 3:30 pm (1930 GMT) on Wednesday, as the ferry was docking at Staten Island after making a regular 25-minute commuter trip from Manhattan.
Witnesses said the ferry hit the dock at high speed and wooden pilings lining the pier punctured the right side of the vessel just above the waterline.
"This is a terrible tragedy ... people on their way home all of a sudden taken from us"
mayor, New York
"Everybody jumped for their lives," Bob Carroll, who was on the boat, told the local NY1 television station.
"The whole side of the boat looked like a can opener had been taken to it. If I had been sitting on the right side of the boat, I'd have been dead. You could see some people were not going to make it."
The ferry had a capacity of about 6000, but it was unclear exactly how many people were on board.
New York fire department spokesman David Billig said dozens of people had been seriously injured, some of them with limbs amputated and had been taken to local hospitals.
"I heard what sounded like an explosion and my first thought was that it was a bomb," said another passenger, retired police sergeant Paul Wiedemann.
"The structure of the boat was ripped open about half or three-quarters of the way down. It seemed that the boat didn't slow down and then the lower side appeared to cave in."