The killing of 84 people celebrating Bastille Day is the worst attack on France since the 13 November attacks last year.
France has been under a state of emergency ever since and security across the country was high, with intelligence services warning of the risk of further attacks.
This is what we know so far.
Panic in Nice
The terror began a little after 22:30 (20:30 GMT) on Thursday, shortly after thousands of people had watched a firework display on the seafront in Nice, at the end of a day marking France’s national holiday, Bastille Day.
There had been a mood of celebration and the crowd had enjoyed an air force display during the evening.
As families strolled along the city’s renowned Promenade des Anglais, a large white lorry careered at full speed towards them. The vehicle mounted the kerb then went back on the road, zigzagging for up to 2km (1.25 miles), as the driver intentionally drove into the crowd.
A local MP spoke of hundreds of people being run over.
Media captionNader el-Shafei saw the final moments of the Nice attack
Police finally managed to bring the lorry to a halt near the luxury Palais de la Mediterranee hotel.
“I was opposite the Palais de la Mediterranee when I saw a lorry at high speed running over people. I saw it with my own eyes, people tried to stop it,” said one witness.
The driver opened fire on people in the crowd, according to local reports. Police fired back and the driver was eventually shot dead. Images from the scene showed the windscreen and front of the lorry raked with bullets. Interior ministry officials said the attacker had been “neutralised”.