DEVELOPING: A large truck drove into a crowd of people who had gathered for a Bastille Day fireworks show Thursday in the southe French city of Nice, killing at least 60 people and injuring 100 more in a terror attack, officials said.

The city's prefect of police told FranceTV Info that the death toll was only an estimation. Another police official told France's BFM TV that the driver of the truck was also dead.

A police spokeswoman, Sylvie Toffin, confirmed the incident was deliberate to the Associated Press, saying "It's an attack."

A witness, Wassim Bouhlel, told the Associated Press that he saw the truck drive into the crowd, then witnessed the driver emerge with a gun and start shooting.

"There was caage on the road," Bouhlel said. "Bodies everywhere."

Nice Mayor Christian Estrosi asked residents to stay where they were immediately following the attack.

There was no immediate claim of responsibility, but but France has recently seen a spate of dramatic assaults from by jihadist groups, including the Islamic State group (ISIS) which straddles Iraq and Syria.

The attack happened at around 10:30 p.m. on the Promenade des Anglais, a major boulevard along the Mediterranean Sea.

Sebastien Humbert, a police prefect for the Alpes-Maritime area told BFM TV the truck traveled "over a long distance, which explains this extremely heavy toll."

The Nice-Matin newspaper quoted one of its reporters as saying the truck driver "mounted onto the Prom and he drove on everyone." The reporter added, "people are ruing, it's panic."

A photo taken by the reporter showed around a dozen people lying in the street, with some being tended to by emergency persoel.

The paper posted an image of the truck on Twitter, captioning it, "The truck that drove into the crowd."

July 14 is a national holiday in France that commemorates the storming of the Bastille prison in Paris and the start of the French Revolution.

The Associated Press contributed to this report.