France has declared three days of national mourning after at least 84 people were killed in the city of Nice when an attacker drove a lorry into a large crowd celebrating the country's main national holiday.

Speaking from Nice on Friday, French President Francois Hollande said around 50 people are in critical condition, still "between life and death" after the attack.

Police have identified the suspect on Friday as Mohamed Lahouaiej Bouhlel, a 31-year-old man, who is originally from Tunisia. Authorities said he was married with three children.

IN PICTURES: A night of carnage in the French Riviera

Authorities said Bouhlel, who works as a driver in Nice, rented the lorry he used in the attack five days ago. Bouhlel was known to French police, but not intelligence officials.

The suspect was shot dead on Thursday night, after ramming the lorry through the festive crowd for two kilometres, sending hundreds of people fleeing in terror and leaving the area strewn with bodies, including many children.

Speaking after an emergency meeting on Friday, Prime Minister Manuel Valls said the period of national mourning would begin on Saturday.

Valls also confirmed that a measure extending the country's state of emergency, which has been in force since the November 13 Paris attacks, would go before parliament next week.

"Times have changed, and France is going to have to live with terrorism, and we must face this together," he said.

'Nothing will make us yield'

There was no immediate claim of responsibility for what was the third major attack to hit France in the past 18 months.

Hollande said the incident had "all the elements to be called a terrorist attack" and vowed to fight similar threats.

"Nothing will make us yield in our will to fight terrorism," he said in the early hours of Friday.

READ MORE: Hollande and world leaders condemn Nice attack

"We will further strengthen our actions in Iraq and in Syria. We will continue striking those who attack us on our own soil," Hollande added, in reference to France's involvement in a coalition of nations carrying out air strikes against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group.

As condolences poured in from around the world, more details emerged about the attack that began shortly after the end of a firework display for Bastille Day.

Footage showed a scene of horror up and down the promenade, with broken bodies splayed on the asphalt - some piled near one another, others bleeding on to the roadway or twisted into unnatural shapes.

Some people at the promenade had tried to escape into the water, local MP Eric Ciotti said on Friday, giving new details of the horrifying last minutes of the attack.

"A person jumped on to the truck to try to stop it," Ciotti told Europe 1 radio.

"It's at that moment that the police were able to neutralise this terrorist. I won't forget the look of this policewoman who intercepted the killer."

Al Jazeera's David Chater, reporting from Nice, said people in the city were "absolutely distraught".

PEOPLE AND POWER: Backlash - France's New Hard Line on Terror

"This was a horrific attack. The lorry was driven at speed; it was swerved around the road and it was used to crash, maim, kill and injure," he said.

"All the families who'd gathered on this road, they had just finished seeing the Bastille Day fireworks, and so it was an extraordinarily calculated attempt at mass murder and an attempt that did succeed."

'Bodies everywhere'

The Paris prosecutor's office opened an investigation for "murder, attempted murder in an organised group linked to a terrorist enterprise". The investigation was being handled by France's intelligence agency and judicial police.

Police also said investigations were under way to find out if the driver acted alone or if he had accomplices at the scene.

A witness told the Associated Press news agency he saw the driver emerge from the lorry shooting, after ramming into the crowd.

"There was carnage on the road," Wassim Bouhlel, a witness, told AP. "Bodies everywhere."

In a video viewed more than 2,500 times on Facebook, a trembling Tarubi Wahid Mosta told of the horror on the promenade, where he took photos of an abandoned doll and pushchair and came home with a victim's dog.



"I almost stepped on a corpse. It was horrible. It looked like a battlefield," he said.



In a series of posts he described his sense of helplessness when faced with the carnage.



"All these bodies and their families ... they spent hours on the ground holding the cold hands of bodies dismembered by the truck. You can't even speak to them or comfort them."