A suspected terrorist ploughed into a crowd celebrating Bastille Day in Nice, southern France on Thursday evening, leaving more 80 people dead.
Here's everything we know so far.
An armed man, later identified as Mohamed Lahouaiej Bouhlel, drove a huge lorry at speed into a large crowd on the seafront Promenade des Anglais.
The attack took place as a fireworks display marking the French national day ended at around 10:30pm local time.
Bouhlel is said to have zigzagged along the seafront and knocked people down "like skittles". He was shot dead after reportedly exchanging fire with police.
Weapons and grenades were found inside the lorry
How many people died?
At least 84 people - including many foreigners and 10 children - were killed.
There are fears the death toll could rise further with 18 of 85 people who remain in hospital still critically ill, including one child.
Foreign Secretary Boris Johnson confirmed that at least one British national had been injured.
Who was the attacker?
Mohamed Lahouaiej Bouhlel was a 31-year-old Tunisian who had lived in France for 10 years.
He was married with three children but was estranged from his wife Jean-Yves Garino who told local media he had been physically abusive. She was arrested by police investigating the attack but has since been released.
Bouhlel reportedly drove along the route of the seafront promenade twice in the days before the attack in preparation.
Initial investigations have indicated that the delivery driver had links to extremism, according to French Prime Minister Manuel Valls, who said he was radicalised "very quickly".
Was anyone else involved?
It is not yet know if Bouhlel acted alone or if any others were involved in plotting the attack, however seven people have been arrested over the attack.
What have eyewitnesses said?
Footage captured the panic as people fled the scene and eyewitnesses described a "scene of horror" with "bodies everywhere".
Pavements were seen smeared with dried blood with smashed children's pushchairs lying nearby.
"People went down like ninepins," a restaurant owner told local media.
A journalist said: "Bodies every five metres, limbs ... blood."
How has the French government reacted?
The French president was visiting Avignon at the time of the attack but returned to Paris to hold a crisis meeting.
In a pre-dawn televised address to the nation, Hollande said the incident was a "terrorist assault" and the assailant had the sole intention of "killing, crushing and massacring."
"And they were struck - struck dead to satisfy the cruelty of an individual, and maybe a group."
Hollande has extended France's state of emergency, which was due to expire on July 26 following the Paris attacks, by three months.
And he said the country's borders were being tightened, as he vowed that France would show "real force and military action in Syria and Iraq".
France declared three days of mourning following the atrocity.
How has the world reacted?
President Obama led the worldwide condemnation, saying it "appears to be a horrific terrorist attack".
New Prime Minister Theresa May said "we must redouble our efforts to defeat these brutal murderers".
Foreign Secretary Boris Johnson said he was "shocked and saddened" by the "appalling attack".
German Chancellor Angela Merkel said Germany stood on the side of France and many others in the fight against terrorism.
US Democratic presidential hopeful Hillary Clinton said terrorists had struck one of the United States' "closest allies in Europe, attacking families celebrating the history and culture of their country on Bastille Day".
Ex-French president Nicolas Sarkozy said he felt "deep emotion and infinite sadness" after the attack.
What is Bastille Day?
Bastille Day is France's national day, marking the start of the 1798 revolution.
The day marks the occasion when the Bastille prison was stormed by protesters against the autocratic rule of King Louis XVI.
France targeted yet again
A string of atrocities, most inspired by so-called Islamic State, over the past 18 months has left more than 200 people dead and injured hundreds more.
"We should learn to live with terrorism," the French prime minister said on Friday.
Government criticised over national security
In the wake of this latest terror attack, the French government has faced criticism over national security.
Former President Nicolas Sarkozy has accused the government of bad policies which he says failed to prevent three major attacks in the past 18 months.
A poll conducted four days after the attack in Nice found two-thirds of French people do not trust their government in the fight against terrorism.
French Prime Minister Manuel Valls was greeted by boos and calls to resign as joined thousands at the Monument du Centenaire for a minute's silence.