Here is what we know about what French President Francois Hollande has declared an "undeniable" terrorist attack.
How did the attack unfold?
The large white truck plunged into the crowd at around 11:00pm (2100 GMT) Thursday night as hundreds of people were on Nice's beachfront Promenade des Anglais to watch the fireworks for France's national day.
Christian Estrosi, head of the local region, said guns and "larger weapons" were found in the truck.
Interior minister Bernard Cazeneuve told reporters 84 people had been killed after the truck ploughed two kilometres (1.3 miles) through the crowd, who had just finished watching the firework show.
As rumours swirled online, interior ministry spokesman Pierre-Henry Brandet dismissed reports that people had been taken hostage.
The attacker has been shot dead, Hollande said.
He is yet to be named, but the identity papers of a 31-year-old French-Tunisian were found in the truck, according to a police source. The papers indicate the man is a Nice resident.
There has been no official confirmation that the attacker shot at either the police or the public, though one witness, a man named Nader, told BFM television he saw the driver pull out a gun and start firing at police.
Multiple bullet holes were visible in the truck's windscreen as police moved in after the carnage.
- Was this a jihadist attack? -
The attack has not been claimed by any group, but Hollande said in an address to the nation early Friday that the attack was of an "undeniable terrorist nature".
Prosecutors say the probe will be handled by anti-terrorism investigators.
"Investigations are currently underway to establish if the individual acted alone or if he had accomplices who might have fled," interior ministry spokesman Brandet said.
The attack comes with France under a state of emergency following the Islamic State attacks in Paris in November that left 130 people dead.
How has the government reacted?
Hollande announced that the state of emergency would be extended by three months and army reservists called up to boost security.
He also said France would strengthen its role in Iraq and Syria, where it is part of the international coalition fighting IS jihadists.
He will chair a meeting of top military and security officials later Friday to decide on possible further steps.
Has anything like this happened in France before?
In December 2014, two men ploughed their vehicles into pedestrians in two days -- separate incidents that left France reeling.
The first driver shouted "Allahu Akbar" (God is greatest) as he drove into people in the eastern city of Dijon, injuring 13.
The 40-year-old had a long history of mental illness, and no ties to jihadist groups, the government said.
A day later, a man rammed a white van into a Christmas market in the western city of Nantes, killing one person and injuring nine others. He then stabbed himself several times.
Prosecutors said a notebook was found in his vehicle in which he spoke of his "hatred for society" and said he feared "being killed by secret agents".
The man committed suicide in his prison cell in 2016 while awaiting trial.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.