Interior Minister Bernard Cazeneuve said 80 people died and 18 were in a critical condition. Many more were also wounded in the attack along the famed seafront Promenade des Anglais as the fireworks ended just after 10:30pm (2030 GMT).
The driver also opened fire before police shot him dead.
In a pre-dawn address to the nation, President Francois Hollande said he was calling up military and police reservists to relieve forces worn out by an eight-month state of emergency begun after the Islamic State militant group killed 130 people in Paris.
The state of emergency was extended by three months.
"France is filled with sadness by this new tragedy," Hollande said, noting several children were among the dead in what he said he had no doubt was an act of terrorism.
