At least 84 people were killed and over 100 injured, among them 20 seriously, on Thursday night after a truck plowed into a crowd in the French city of Nice.
Eyewitnesses said the driver picked up speed to slam the lorry into people who were celebrating Bastille Day along the city's famous Promenade des Anglais.
There are unconfirmed reports that he then emerged from the vehicle and started shooting.
The French newspaper Le Figaro reported that weapons were found on the truck following the attack.
No group has thus far claimed responsibility for the attack, but French prosecutors said the probe would be handled by anti-terrorism investigators.
The Chabad emissary to Nice, Rabbi Yosef Pinson, told Israeli media on Friday morning that one member of the Jewish community was injured in the attack. No details were provided as to his condition.
One image on Twitter showed about a dozen people lying on the street, some being tended to, according to the BBC.
A journalist with the Nice Matin newspaper reported from the scene that there was "a lot of blood and without doubt many injured".
President of the Nice, Cote d'Azur region, Christian Estrosi, tweeted shortly after the incident, "The driver of a lorry seems to have killed dozens of people. Stay in your homes. More information to follow..."