France has been stunned again as a large white truck mowed through a crowd of revelers gathered for a Bastille Day fireworks display in the Riviera city of Nice, killing at least 80 and leaving what one witness said was "bodies everywhere."

The attack Thursday night on France's national holiday rocked a nation still dealing with the shock of the attacks last November in Paris that killed 130.

Flags were lowered to half-staff in Nice and in Paris.

Interior Minister Bernard Cazeneuve, who traveled to the scene, said another 18 people were seriously hurt. He said police were trying to determine the driver's identity, refusing to confirm reports an ID card had been found in the truck.

French media broadcasts showed partiers in summer apparel running for their lives down Nice's palm tree-lined Promenade des Anglais, the famous seaside boulevard named for the English aristocrats who proposed its construction in the 19th century.

"France was struck on the day of its national fete, July 14, the symbol of liberty," a somber President Francois Hollande, said on national television early Friday, denouncing "this monstrosity" — a truck bearing down on citizens "with the intention of killing, smashing and massacring ... an absolute violence."

"The terrorist character (of the attack) cannot be denied," he said. "All of France is under the threat of Islamic terrorists."

Hollande said a state of emergency — which was to have ended July 26 — would be extended for three months. First imposed after the November attacks, it has been renewed every three months.

Police killed the driver of the truck in what witnesses on French TV said was a hail of bullets, but Hollande said it was not immediately clear whether he had accomplices. The Paris prosecutor's office opened an investigation for "murder and attempted murder in an organized group linked to a terrorist enterprise."

France has lived with soldiers in the streets since the November attacks, and just days ago authorities beamed with price at the close of the month-long European football championships that ended July 10 without incident.

Wassim Bouhlel, a Nice native, told The Associated Press that he saw a truck drive into the crowd. "There was carnage on the road," he said. "Bodies everywhere." He said the driver emerged with a gun and started shooting.

Sylvie Toffin, a press officer with the local prefecture, said the truck ran over people on a "long trip" down the sidewalk that ended near Nice's Palais de la Mediterranee, a building that fronts the beach.

The president of the Provence Alpes Côte d'Azur region, which includes Nice, said the truck was loaded with arms and grenades, although police have not confirmed that. Christian Estrosi also told BFM TV that "the driver fired on the crowd, according to the police who killed him."

There is still confusion on what exactly happened on a night when thousands were celebrating. Witnesses, mostly unnamed, recounted on French television scenes of horror, with one saying the truck mowed people down like a ball in a bowling alley.

Video footage showed men and women — one or two pushing strollers — racing to get away from the scenes. Photos showed a truck with at least half a dozen bullet holes in its windshield.

Hollande called a defense council meeting Friday with key ministers, and will head to Nice after that.

French Interior Minister Bernard Cazeneuve said "we are in a war with terrorists who want to strike us at any price and in a very violent way."

Hollande announced a series of measures to bolster security. Besides continuing the state of emergency and the Sentinel operation with 10,000 soldiers on patrol, he said he was calling up "operational reserves," those who have served in the past and will be brought in to help police, particularly at French borders.

He reiterated that France is also bolstering its presence in Iraq and Syria, where he said earlier military advisers would be on the ground to help Iraqis take back the Islamic State stronghold of Mosul.

President Barack 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.

Writing online, Nice Matin journalist Damien Allemand 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 said.

"I saw bodies flying like bowling pins along its route. Heard noises, cries that I will never forget."

Graphic footage showed a scene of horror up and down the Promenade, with broken bodies splayed out on the asphalt, some of them piled near one another, others bleeding out onto the roadway or twisted into unnatural shapes.

"Help my mother, please!" one person yells out on the video. A pink girl's bicycle is briefly seen overturned by the side of the road.

Details of the footage could not immediately be verified.

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Ganley reported from Paris.

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Associated Press writers Raphael Satter in Paris, Naomi Koppel in London and Josh Replogle in Miami contributed to this report.