An eyewitness has described the scene as a lorry drove in to crowds on the Promenade des Anglais.
Nadar El Shafei thought the driver had "lost control" of the vehicle at first and had hit pedestrians "by accident".
"I kept yelling at him and shouting at him to stop", he told 5 live's Clare McDonnell.
"He picked up something that looked like a cell phone and I thought he was calling for an ambulance...but he started to shoot through the window".
At least 84 people have died, including children, after a lorry pthrough a crowd celebrating Bastille Day in the southern French city of Nice.
The driver drove through crowds for 2km (1.2 miles) on the Promenade des Anglais at about 23:00 local time, before being shot dead by police.
