The driver was shot dead after barrelling the truck two kilometres (1.3 miles) through the festive crowd on the palm-lined Promenade des Anglais, sending hundreds fleeing in terror and leaving the area strewn with bodies.
Authorities said they found identity papers belonging to a 31-year-old French-Tunisian citizen in the truck, as well as "guns" and "larger weapons".
"France was struck on its national day ... the symbol of freedom."
The attack was of an "undeniable terrorist nature," a sombre Hollande said in a televised national address, confirming that "several children" were among the dead as families came together to celebrate France's national day.
The bloodshed came on Bastille Day, a celebration of everything France holds dear, its secular republic and the values of "Liberte, Egalite, Fraternite" (Freedom, Equality, Fraternity)..
"France was struck on its national day ... the symbol of freedom," said Hollande.
A photograph showed the front of the truck riddled with bullet holes and badly damaged, with burst tyres. A lone doll lay abandoned on the promenade where families celebrated the holiday just hours earlier.
