No fewer than 30 persons on Thursday night confirmed dead when a lorry struck a crowd during Bastille Day celebrations in the southern French city of Nice.
The incident took place on the famous Promenade des Anglais during a firework display, media reports say.
One image on Twitter showed about a dozen people lying on the street, some being tended to.
The local prefecture has urged people in the area to remain indoors, calling the incident “an attack”.
Nice Mayor Christian Estrosi said that “a lorry driver appears to have killed dozens of people”.
Sebastien Humbert, the prefect of the Alpes-Maritimes region, told France’s BFM TV that “perhaps about 30 people” were dead and 100 injured.
He said the lorry driver had been shot dead.
The mayor and police urged residents to stay indoors.
Some reports spoke of shots being exchanged between police and the occupants of the lorry but these have not been confirmed.
Social media video showed people running through the streets in panic following the incident.
A journalist with the Nice Matin newspaper reported from the scene that there was “a lot of blood and without doubt many injured”.
An Agence France-Presse reporter said the incident took place as the firework display was ending, adding: “We saw people hit and bits of debris flying around.”
Another image on Twitter showed a white lorry stopped in the middle of the promenade with damage to its front, and four police officers observing it while taking cover behind a palm tree.
One eyewitness told BFM TV: “Everyone was calling run, run, run there’s an attack run, run, run. We heard some shots. We thought they were fireworks because it’s the 14th of July.
“There was great panic. We were running too because we didn’t want to stick around and we went into a hotel to get to safety. ”
Another witness, Roy Calley told the BBC that there were “thousands of people on the promenade” when the incident happened.