At least 84 people have been killed - several of them children - after a lorry driver ploughed into crowds celebrating France's national Bastille Day in Nice.
French President Francois Hollande has described the attack as a "terrorist crime".
Northern Ireland tourists in the popular holiday destination in the south of France have described the chaos and confusion as the attack unfolded.
French President Francois Hollande said about 50 people are "between life and death" after the Nice attack.
He said: "As I'm speaking, 80 people are dead, 84 people to be precise, and there are some 50 people in a critical condition, between life and death.
"Among these victims, there are French, there are also a lot of foreigners from all continents and there are many children, young children.
"They came to see fireworks with their families, to be happy, to share in something joyous, something dazzling and were struck - struck dead to satisfy the cruelty of an individual, and maybe a group."
He added that the battle against terrorism will be long because the enemy will continue to attack Western values.
He made the comments on Friday after he was briefed, alongside Prime Minister Manuel Valls, on the situation by police and military representatives in Nice.
Belfast's Lord Mayor and deputy Lord Mayor have opened a book of condolence for those killed in last week's lorry attack in Nice, France.
The Irish Department of Foreign Affairs is "urgently following up" on concerns for the safety of Irish citizens in Nice.
UTV journalist and producer Ben Terry, who was in Nice at the time of the attacks, has described a scene of “mass panic”.