"There are French among the victims and also many foreigners from every continent and many children, young children," said a clearly moved Hollande in a speech from a hospital in the French Riviera city.
"As I speak 84 people are dead, and around 50 are in a critical condition between life and death," he added.
Witnesses said a truck drove at speed into a crowd for two kilometres (1.3 miles) after around 30,000 people had been watching a fireworks display on France's national day.
Hollande previously described the attack on the palm-lined Promenade des Anglais as being of an "undeniable terrorist nature".
Kerry, Lavrov pay joint Nice tribute
US Secretary of State John Kerry and his Russian counterpart Sergei Lavrov on Friday offered their condolences at the French embassy in Moscow over the Nice truck attack that left at least 84 people dead.
Kerry and Lavrov laid flowers in front of the embassy building and wrote messages in a book of condolences. The top diplomats held a minute of silence for the victims earlier Friday ahead of talks on the Syria crisis.
