Hollande confirmed that 77 people, including some children, were killed when the truck drove through the crowds who had just watched a fireworks display on seafront in the city.
"We, the Malaysian students in France, are truly devastated to learn about the recent attack in Nice on Bastille Day".
I am now in the city, having watched the fireworks in the crowd on La Promenade des Anglais where the attack took place.
Police found identity papers in the cab of the truck belonging to a 31-year-old man who was born in Tunisia but lived in Nice, and had dual French-Tunisian citizenship, according to Reuters.
European Commission President Jean-Claude Juncker said he was "touched and afflicted by the awful ordeal" in Nice.
Interior Minister Bernard Cazeneuve said 80 people died and 18 were in a critical condition, with many more also wounded.
The UK Telegraph reports the truck driver aimed at the crowd, leaving dead and injured people on the street.
US President Barack Obama issued a statement condemning what he said appeared to be "a horrific terrorist attack".
Flags were lowered to half-staff in Nice and in Paris, and Hollande extended the state of emergency imposed after the November bloodshed another three months.
Hollande said he was calling a defense council meeting Friday that brings together defense, interior and other key ministers, then heading to Nice.
The president of the Nice region said at least 60 people were killed.
He also said France would strengthen its role in Iraq and Syria, where it is part of the global coalition fighting IS jihadists.
Hundreds were reported fleeing the scene after the vehicle careered into people who had gathered to celebrate the country's official independence day.
The driver of the truck was shot dead by police, but some witnesses said they thought he was firing a gun as he drove.
Images being broadcast across French media showed people running for their lives down Nice's Promenade des Anglais, the famous seaside boulevard named for the English aristocrats who proposed its construction in the 19th century.
Brits caught up in the massacre in which 84 people were killed when a lorry ploughed into crowds today told of their horror at the scenes.
French President Francois Hollande addressed the public, describing the attack as a "monstrosity", and adding that soldiers would be deployed to support security forces.
A Rihanna concert scheduled for Friday night at the Allianz Riviera stadium in Nice has been cancelled, as have the city's jazz festival which was due to run from Saturday to Wednesday and some of the Bastille celebrations over the weekend.