NICE, France -- A Tunisian citizen legally residing in France drove a truck through crowds celebrating Bastille Day along Nice's beachfront, killing at least 84 people, many of them children. The slaughter ended only after police killed the armed attacker in a hail of bullets.
The attacker has been formally identified as 31-year-old Mohamed Lahouaiej Bouhlel, a Nice resident, CBS News correspondent Elizabeth Palmer reports. He was known to police for petty crimes.
On Friday, French President Francois Hollande said that about 50 people were still "between life and death."
French leaders extended the country's 9-month-old state of emergency and vowed to deploy thousands of police reservists on the streets after Thursday night's massacre of pedestrians leaving a fireworks display for France's national independence day.
Video shot by terrified civilians shows crowds fleeing in panic, leaping off the elevated pavement onto the beach below, and police finally surrounding the stationary truck and fatally shooting its driver.
Wassim Bouhlel, a native of Nice, told The Associated Press he saw a truck drive into the crowd, then its driver emerged with a gun and started shooting.
"There was carnage on the road. Bodies everywhere," he said.
Police said the attacker had drawn a gun on them. The truck's windshield was riddled with bullets.
No group has claimed responsibility for the carnage, but French officials called it an undeniable act of terror. The assault on revelers in the southern French city rocked a nation still dealing with the aftermath of two attacks in Paris last year that killed 147 people and were claimed by the Islamic State of Iraq and Syria, or ISIS.
"Terrorism is a threat that weighs heavily upon France and will continue to weigh for a long time," Prime Minister Manuel Valls said after Hollande called an emergency government meeting Friday. "We are facing a war that terrorism has brought to us. The goal of terrorists is to instill fear and panic. And France is a great country, and a great democracy, that will not allow itself to be destabilized."
Hollande rushed to Nice, 490 miles south of Paris, to offer his condolences after the emergency meeting.
"France was struck on the day of its national holiday, July 14, the symbol of liberty," Hollande said Friday, denouncing "this monstrosity" - a truck bearing down on citizens "with the intention of killing, smashing and massacring."
Hollande said it was not clear whether the driver had accomplices. The Paris prosecutor's office opened an investigation for "murder and attempted murder in an organized group linked to a terrorist enterprise."
The truck knocked over and crushed pedestrians over a distance of 1 1/4 miles, a lawmaker said. Broadcast footage showed a scene of horror along Nice's famous promenade, with broken bodies splayed on the asphalt, some piled near one another, others bleeding onto the roadway or twisted into unnatural shapes.
The regional president, Christian Estrosi, told BFM TV that "the driver fired on the crowd, according to the police who killed him." He said more than 10 children were among the dead, which also included two Americans and people from Russia, Switzerland and Ukraine.
Some people tried to escape into the water, according to Eric Ciotti, a lawmaker who represents Nice.
"A person jumped onto the truck to try to stop it," Ciotti told Europe 1 radio. "It's at that moment that the police were able to neutralize this terrorist. I won't forget the look of this policewoman who intercepted the killer."
Flags were lowered to half-staff in Nice, Paris, Brussels and many capitals across Europe. Hollande announced a three-month extension to the state of emergency imposed after the Nov. 13 attacks on Paris that killed 130 victims. The government declared three days of national mourning to begin Saturday.
Interior Minister Bernard Cazeneuve, who traveled to the scene, said, "We are in a war with terrorists who want to strike us at any price and in a very violent way."
Ciotti said identification papers were found in the truck and that investigators were trying to determine whether they were legitimate.
Partiers in summer apparel ran for their lives down Nice's palm tree-lined Promenade des Anglais, the city's famous seaside boulevard.
Estrosi said some of the city's 1,200 security cameras had pinpointed the moment the attacker boarded the truck, far from the seaside "in the hills of Nice" and could follow his path to the promenade. Estrosi called for the investigation to focus on any accomplices.
"Attacks aren't prepared alone. Attacks are prepared with accomplices," Estrosi said. "There is a chain of complicity. I expect it to be unveiled, discovered and kept up to date."
France has lived with soldiers in the streets since the Nov. 13 attacks in Paris, and much of the country experienced increased security during the monthlong European football championship that concluded July 10.
Damien Allemand, a journalist for the regional newspaper Nice-Matin who was at the waterside, said the fireworks display had finished and the crowd had got up to leave when they heard a noise and cries.
"A fraction of a second later, an enormous white truck came along at a crazy speed, turning the wheel to mow down the maximum number of people," he wrote in an online account. "I saw bodies flying like bowling pins along its route. Heard noises, cries that I will never forget."
On video, one person could be heard yelling, "Help my mother, please!" A pink girl's bicycle was overturned by the side of the road.
Hollande said France would bolster its presence in Iraq and Syria, where he said earlier that military advisers would be on the ground to help Iraqis take back the ISIS stronghold of Mosul.
In Washington, the U.S. State Department confirmed that two Americans were among the dead. President Obama condemned what he said "appears to be a horrific terrorist attack."
European Council President Donald Tusk said it was a "tragic paradox" that the victims of the attack in Nice were celebrating "liberty, equality and fraternity"- France's motto - on the country's national day.
France, one of the world's top tourist destinations, has long known it is a top target for ISIS. In September 2014, then-ISIS spokesman Abu Mohammed al-Adnani referred to "the filthy French," telling Muslims within the country to attack them in any way they could, including "crush them with your car."
France is also ISIS' biggest source for European recruits. Nice was home for a prolific producer of French-language jihadist recruitment videos, a former petty drug dealer named Omar Omsen who is now fighting in Syria.