A gunman at the wheel of a heavy truck ploughed into crowds celebrating Bastille Day in the French city of Nice, killing at least 84 people and injuring scores more.

The attack - which President Francois Hollande called a terrorist act - is the third mass killing in France since attackers targeted a kosher supermarket and the offices of the satirical magazine Charlie Hebdo in January 2015.

Seventeen people died in Paris in three days of violence that began with the attack by two Islamist gunmen on the offices of Charlie Hebdo on Jan. 7 - in which 12 people were killed - and ended with a siege at a kosher supermarket two days later.

In November, nine militants killed a further 130 people and wounded hundreds more in a number of attacks across Paris.

Some assailants blew themselves up near the Stade de France stadium, others opened fire on downtown cafe terraces and a third group armed with guns and suicide vests killed 90 music fans at the Bataclan rock concert hall.