Six victims were pronounced dead at the scene, while two more died at a nearby hospital. At least 11 others were injured when the truck struck in Manhattan.
The driver, identified by police as Sayfullo Saipov, 29, from Uzbekistan, was shot by police after jumping out of the vehicle with what turned out to be two fake guns.
He was taken to hospital and is in police custody.
Hours after the attack, the names of the first victims emerged as Argentina's foreign ministry said Hernan Diego Mendoza, Diego Enrique Angelini, Alejandro Damian Pagnucco, Ariel Erlij and Hernan Ferruchi had died.
The group were marking three decades since their graduation from Polytechnic College in the city of Rosario in central Argentina.
A sixth Argentinian man with the group, Martin Ludovico Marro, was taken to the Presbyterian hospital in Manhattan.
New York Truck attack
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According to La Capital newspaper, the group of 10 friends were exploring Manhattan on bicycles when the attack took place.
They had left Argentina for the US on Saturday, first visiting one of their friends in Boston before moving on to New York.
An unnamed Belgian woman was also among the dead, the country's deputy prime minister said.
Two further victims are currently unidentified.
New York attack: Man 'drove truck into school bus with children inside'
Argentina's president Mauricio Macri tweeted: "Profoundly moved by the tragic deaths this afternoon in NY. We are at the disposal of the families of the Argentinian victims."
Foreign minister Jorge Faurie said that his heart was with the family and friends of those who had died "at this moment of deep and inexplicable pain".
New York mayor Bill de Blasio described the attack as "a particularly cowardly act of terror" while governor Andrew Cuomo said it was a "lone wolf" attack, and there was no evidence it was part of a wider plot.
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