An attacker killed at least 84 people by driving a truck at high speed into crowds watching Bastille Day fireworks in the French Riviera city of Nice late on Thursday. French President Francoise Hollande said the attack was undeniably of a terrorist nature, according to a Reuters translation of the president's televised national address at 4 a.m. local time. The act was a "monstrous" one, he said, and the victims included "many children." Police shot and killed the driver, who drove a 25-ton, unmarked truck at high speed for more than 100 meters along the famed Promenade des Anglais seafront in the southern resort town before hitting a mass of spectators, regional sub-prefect Sebastien Humbert had earlier told France Info radio. The driver then continued to plow on through the crowd for hundreds of meters as "people went down like nine-pins," according to an onlooker.

The incident occurred around 10.40 p.m. local time. Photographs of the truck show its windshield scored by bullet holes and its front grille destroyed. NBC News cited a source as saying that the driver, who has not yet been named, was a French national of Tunisian descent. French media made similar reports, while Reuters reported that the man was 31 and born in Tunisia, adding that he was known to police for common law crimes but not to intelligence services. Reuters was citing an unnamed police source. The death toll from the attack had mounted throughout the evening and early morning in France, with the latest count coming at about 8 a.m. CEST, when a spokesman for the Interior Ministry said 84 people had died and 18 were in critical condition. CNBC was unable to independently confirm the numbers. Among the casualties were a father, 51, and son, 11, from Lakeway, near Austin in Texas, NBC News said.

A truck ploughed into a crowd in the French resort of Nice on July 14, leaving at least 60 dead and scores injured in an 'attack' after a Bastille Day fireworks display, prosecutors said on July 15, 2016. Valery Hache | AFP | Getty Images

In his TV address, Hollande said a state of emergency that had been due to expire on July 26 would be extended by three months. The president also said that the country would maintain the 10,000-strong homeland security force that had been protecting France during an eight-month state of emergency, and that he would call up military and police reservists to help relieve the existing forces. Hollande will travel to Nice on Friday to support the region. According to Reuters, regional president Christian Estrosi told BFM TV that the driver had also opened fire on the crowd and that weapons and grenades were found inside the truck after the attacker was killed by police.

Humbert described it as a clear criminal attack. Residents of the Mediterranean city close to the Italian border were advised to stay indoors. There was no sign of any other attack, nor any immediate claim of responsibility. @Gendarmerie: #Nice06 Emergency operation in progress. Keep calm and avoid downtown area. Follow the official accounts to be informed. Almost exactly eight months ago Islamic State militants killed 130 people in Paris on Nov. 13, the bloodiest in a number of attacks in France and Belgium in the past two years. Four months ago, Belgian militants linked to the Paris attackers killed 32 people with a series of bombs in Brussels, while just a month ago a man who said he was affiliated with Islamic State killed a police captain and his female partner at their house in a Paris suburb. On Sunday, France had breathed a sigh of relief as the month-long Euro 2016 soccer tournament ended without a feared attack. Hollande called the latest carnage an attack on liberty by fanatics who despised human rights, but said that France would continue its military operations in Syria and Iraq.

"We thought he lost control. We all shouted: 'Stop! Stop!'" said Nader Shafa'ai, an Egyptian tourist, who captured the mayhem on his video camera as the truck came careening through the crowd. "Then it was clear it wasn't an accident." The footage Shafa'ai shot shows French police as they surrounded the white truck and fired rounds at the driver. The footage also shows scores of bodies under and behind the truck. "I filmed it because I was in shock," he said. One woman told France Info she and others had fled in terror: "The lorry came zig-zagging along the street. We ran into a hotel and hid in the toilets with lots of people."



Police officers and rescue workers arrive to assist the crowd that a truck drove through during Bastille Day celebrations in Nice, France. Valery Hache | AFP | Getty Images

Regional newspaper Nice Matin quoted its own reporter at the scene saying there were many injured people and blood on the street.

Damien Allemand, the paper's correspondent, was quoted as saying: "People are running. It's panic. He rode up onto the Prom and piled into the crowd ... There are people covered in blood. There must be many injured." Social media carried images of people lying apparently lifeless in pools of blood, prompting some people to suggest that users do not post photographs and videos of the dead and injured. Awful news about #Nice and shocking to see so many graphic videos when police haven't had time to contact relatives yet. Come on Twitter!

A truck drove through a crowd during Bastille Day celebrations in Nice, France. CNBC

Hollande had just hours earlier told reporters that a state of emergency put in place after the Paris attacks in November would not be extended when it expired on July 26.

"We can't extend the state of emergency indefinitely, it would make no sense. That would mean we're no longer a republic with the rule of law applied in all circumstances," Hollande told journalists in a traditional Bastille Day interview. U.S. President Barack Obama condemned what he said "appears to be a horrific terrorist attack." "I have directed my team to be in touch with French officials, and we have offered any assistance that they may need to investigate this attack and bring those responsible to justice," Obama said in a statement. "We stand in solidarity and partnership with France, our oldest ally, as they respond to and recover from this attack."

European Council President Donald Tusk said the attack was in contrast to the history of Bastille Day, France's national day, that celebrates the storming of the Bastille, a key event in the French Revolution. Tragic paradox that the subject of #NiceAttack was the people celebrating liberty, equality and fraternity.

Canadian Prime Minister Justin Trudeau said that Canada has offered "all possible assistance" to the French government. "Senseless acts like this one are not isolated events, and we will continue to work with our allies and partners to fight terrorism in all of its forms. We will bring those who are responsible to justice, whether they be the perpetrators, or those involved in funding or organizing such attacks," Trudeau said in a statement.