NICE, France — A Frenchman of Tunisian descent 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.

French leaders on Friday 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 identified the attacker as a 31-year-old Nice resident and said he 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 extremist group.

“Terrorism is a threat that weighs heavily upon France and will continue to weigh for a long time,” Prime Minister Manuel Valls said after French President Francois 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, 690 kilometers (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 two kilometers (1 ¼ 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 police were trying to identify the driver. “We are in a war with terrorists who want to strike us at any price and in a very violent way,” he said.

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.”