The attack was launched on the popular beachfront Promenade des Anglais, which would normally be packed with tourists and residents on a sunny afternoon in July.
But on Friday, screens blocked off more than a mile of the famous boulevard as authorities removed bodies and evidence from the bloody attack.
Just before the carnage Thursday night, hundreds, if not thousands, had gathered on the promenade to watch a colorful display of fireworks and live music for the national holiday.
But as the last firework fizzled, gunfire rang out -- authorities and witnesses say the driver shot from the cab of the truck -- and the truck accelerated down the crowded street.
And again, for the third time in 18 months, a battered France will fly its flags at half-staff to mourn the victims of yet another deadly terrorist attack on its soil. Hollande declared a national mourning period from Saturday to Monday.
Crews covered the dead in the street with blue sheets so emergency vehicles could both avoid running over them and spot them for evacuation.
Slowly, authorities are putting names to the bodies. Three Germans are among the dead, Mayor Reinhard Naumann of Berlin's Charlottenburg-Wilmersdorf district said in a statement. They were all women -- two students and a teacher from the Paula-Fürst-School.
"They were just about to graduate at our school, completing the German A levels. We mourn with the parents of the school, their relatives and their friends," the statement said. "We stand with them side by side and we will provide all the necessary support that is now needed."
Americans Sean Copeland, 51, and his son, Brodie, 11, of Texas were also killed in the attack, the Austin American-Statesman reported, citing a statement from the family. U.S. officials confirmed that at least two Americans were killed in the attack, but did not name them.
Apart from those confirmed dead, three Australians, two Chinese and one British national were injured, officials said.
Learn to live with terrorism
France was just preparing to lift its state of emergency, which was put into place in the wake of the November terror attacks in Paris that killed 130 people, the worst attack in France's history.
The state of emergency would have expired later this month, but Prime Minister Manuel Valls said Friday that a bill to extend it would be submitted to parliament by Tuesday.
"France has been struck once again in her flesh, on the 14th of July, on the day of our national celebration," The attacker wanted to "harm the very idea of national unity," he said, adding grimly that France will have to "learn to live with terrorism."
No group has claimed responsibility for the attack. A source close to the investigation tells CNN that the assailant was known to authorities for petty crime violations, based on a provisional identification of the attacker. French authorities had not opened a counter-terrorism surveillance file on him and he was not known to them for jihadism or Islamist extremism.
According to witnesses and a blurry cell phone video, the white truck rolled purposefully toward the crowds just after the fireworks display finished. The video shows the vehicle accelerating as people scattered in front of it and a few people chased it from behind.
The truck plowed through the crowds for more than a mile before police were able to intervene and fatally shoot the driver.
Andy McArdy told CNN he saw the truck driving at high speed along the promenade and the driver "was firing a machine gun while driving." He said everyone ran, many into a restaurant.
"They didn't know where to go, they were looking for an exit -- they were hoping they'd find an exit out the back. They had to stay there for a couple of hours, but people wouldn't even come out -- they were so frightened -- until the police came and said it was OK to come out," he said.
Tired of attacks
Nice is just the latest city to be hit by a terror attack. Istanbul, Orlando, Baghdad, Brussels and Dhaka in Bangladesh are among targets hit in recent months.
Twitter user Rabia Chaudry described the recent attacks as "a global, asymmetric war that can't be won."
One user claimed "Je suis Nice," using the phrase that was adopted when staff at the French satirical magazine Charlie Hebdo were gunned down in a coordinated shooting in January 2015.
Landmarks around the world were once again lit up in blue, white and red, as they were after the deadly attacks in the French capital in November.
Witnesses describe horror
Eric Dartell was eating at a restaurant on the street where the attack was launched.
"You can see wreckage all along the way: a body, bicycles, street lamps and debris everywhere," he said.
American Dominique Molina, who was watching from a balcony, said the fireworks had just ended and the crowd on the beach was dispersing.
"People were flooding the streets, just walking away from the show, and I heard a lot of loud noises and people were screaming and so to the west, a big moving truck was driving on the promenade, just barreling over people and hitting -- running people over." She estimated the truck moved at 20 to 25 mph.
A tourist from Dallas, Kristen Crouch, lamented the climate of violence that spans the globe, from her hometown to the French city, which she was visiting for a friend's wedding.
"It's really sad when you've been marked safe twice on Facebook in the last week. We shouldn't live in a world like that," she said.
'Big step back'
CNN terrorism analyst Paul Cruickshank said "no country in the western world is threatened more by jihadis and terrorism than France."
"This is a big step back here. They are absolutely exhausted after a year and a half of intense efforts to try and protect this country," Cruickshank said.
"The painful reality here is that if it wasn't going to be this promenade, it would have been any other promenade."
France had put intense security in place for Euro 2016
, the international soccer tournament that just ended. No major attacks occurred during the event.
While the police response to Thursday's attack appeared to be speedy, questions are now being raised about how the man was able to breach security at the event.
Authorities found several fake rifles and fake grenades inside the truck, according to BFM-TV reporter Cecile Ollivier. A 7.65 caliber handgun was found on the attacker who was known to authorities for weapons possession crimes, but nothing terror related, according to Ollivier.
Interior Minister Bernard Cazeneuve said he was deploying 70 police, medical and technical specialists in order to make sure that the remains of those killed were quickly returned to the families. Hospitals in the city have launched an urgent appeal for blood donors.
Leaders around the world have denounced
the brutal incident.
U.S. President Barack Obama issued a statement saying, "We stand in solidarity and partnership with France, our oldest ally, as they respond to and recover from this attack."
The presumptive nominees for the U.S. presidential election also reacted
to the attack, taking strikingly different tones.
Republican Donald Trump said he'd ask for a declaration of war against ISIS while the Democrat candidate-in-waiting, Hillary Clinton, called for greater intelligence gathering to fight terror groups.
The United Nations condemned the "barbaric and cowardly" terror attack.
The U.S. Consulate in Marseille advised U.S. citizens in Nice to call family and friends to notify them that they are safe. The consulate said it was working with authorities to determine whether any U.S. citizens were injured.
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CNN's Christiane Amanpour, Paul Cruickshank, and journalists Cristiana Moisescu and Bianca Britton contributed to this report.