Tearful holidaymakers have gathered near the scene of the Nice massacre as they remembered victims killed when a lorry ploughed along the city's waterfront promenade.
France is in mourning as people come to terms with the shock of the terror attack on Bastille Day which left at least 84 dead and 202 people injured.
The Queen added her voice to the wave of sympathy from leaders across the world as the country faced another terrorist attack, following those in Paris in November, in which 130 died, and in January 2015 in which 17 were killed.
French detectives are still trying to piece together the circumstances after a terrorist deliberately drove a lorry into revellers enjoying a fireworks display on the Promenade des Anglais, before being fatally wounded in a stand-off with armed police.
President Francois Hollande said 50 people were "between life and death", while several people were among the missing and a "small number" of Britons were injured.
The Foreign Office on Friday night described the carnage as a "terrorist attack", causing multiple casualties, and updated its advice for Britons in Nice.
The new advice said: "If you're in the area, follow the instructions of the French authorities, who have cancelled a number of public events planned for the coming days, closed the Promenade des Anglais and a number of the public beaches in and around Nice, and implemented some traffic restrictions."
A vigil took place at Nice Cathedral on Friday night and mourners also gathered at a makeshift memorial amid a visible police presence near the promenade, which is closed to the public.
Eyewitnesses said the Nice attacker - reported to be 31-year-old Mohamed Lahouaiej Bouhlel, a man of French-Tunisian origin not known to intelligence services - swerved from side to side to kill as many people as possible as he drove for a mile along the promenade on the seafront of the city on the French Riviera.
He is said to have pulled a gun from the cab of his lorry in the premeditated attack before being shot dead by police, with people fleeing into the sea in a bid to escape.
French authorities on Friday night confirmed 202 people were wounded, 25 of whom were on life support, while 52 were in a critical condition.
Revellers in the resort initially thought the commotion was part of a celebratory firework display, but then saw the lorry and assumed the driver had lost control.
Jan Jeffreys and her partner Les Smith, from Shropshire, were enjoying their first evening in Nice when the attack happened.
They described a chaotic scene as people tried to run out of harm's way.
Ms Jeffreys, 53, told the Press Association: "There were people in cars turning round on grass verges, reversing. It was just mayhem."
Mr Smith said he was haunted by images of bodies lying in the street.
The 63-year-old businessman said: "The first body that I saw was covered in a sheet and was quite obviously a heavily pregnant woman. It was very upsetting. I keep seeing it. I just can't understand why this happened."
Another couple from Dungannon, Co Tyrone, said they saw a mood of celebration turn to one of fear as they watched the tragedy unfold from their holiday apartment balcony.
Philip Rodgers, 67, in the city with his wife Yvonne, described "tremendous fireworks, crowds and crowds of lovely families, then panic. Very, very frightening". He said it went from "pure happiness to fear".
Prime Minister Theresa May has said Britain must redouble its efforts to defeat "brutal" terrorist "murderers", while police forces across England and Wales have been told to review security at major events over the next week in the wake of the bloodbath.
Foreign Secretary Boris Johnson, who had celebrated Bastille Day with dinner at the French embassy in London, described the attack as "appalling and cowardly".
The Association of British Travel Agents (Abta) issued a statement encouraging people to check with their tour operators before heading to France.
There was a lengthy queue for passport control as passengers landed at Nice airport on flights from London on Friday evening.