84 people were killed on Thursday night when a large truck mowed through a crowd celebrating Bastille Day in Nice. French President Francois Hollande said the truck attack was of a "terrorist character".
In a press conference on Friday morning, Hollande said "the state of emergency was extended in the country for three months beyond July 26".
The driver shot into the crowd and then drove for two km along the pavement of the Boulevard des Anglais, the main street in Nice, mowing down people who had gathered to watch fireworks, regional President Christian Estrosi told CNN affiliate BFMTV.
Police shot and killed the driver, said Pierre-Henry Brandet, a spokesman for the French Interior Ministry.
Firearms, explosives and grenades were found in the truck, Estrosi said.
The driver is suspected to be 31-year-old man of Tunisian origin. The identity papers of a French-Tunisian were found in the truck, reports said quoting police source.
According to the reports, gunmen exchanged shots with police before plowing into the crowd of revellers. Footage captured by terrified bystanders fleescene has captured the sound of several gunshots being fired.
The eye witnesses said they watched the scene in disbelief.
"All we see is this truck along the boardwalk, just ploughing through people, just bodies getting hit and people running in all directions," Tony Molina, who witnessed the attack from his apartment, told CNN.
He said that following the crash, there was a "barrage of gunfire".
"There were families just laying down, crying next to these bodies. Then they had to clear the area out. The bodies stay there covered up," Molina said.
Paul Delane, an American who witnessed attack, was with his partner at the Nice celebration. They had just finished watching the fireworks show and decided to walk towards the other festivities where a DJ was playing music.
"All of a sudden, thousands of people started running in one direction. My partner took my hand immediately and we started running.
"I had no idea what was going on.The music was so loud, we couldn't hear anything. I didn't see a truck, I just heard people running, screaming and crying and people carrying their children.
"I didn't know if I should hide or continue running.
"I wasn't sure what to do, in that situation. No one knew what was going on. We just knew we had to run for our lives."
Over 150 people were also injured in the mayhem.
Hollande and Prime Minister Manuel Valls were in the inter-ministerial crisis cell after the attack, a spokesperson for the Elysee said.
"France was struck on its national day ... the symbol of freedom," said Hollande.
"We must do everything so that we can fight against the scourge of terrorism," he said. "This is France, which is under the threat of Islamist terrorism."
Hollande earlier cancelled his trip to Avignon in the south of the country to return hastily to Paris.
From 9.00 a.m. (local time), Hollande will preside over a security and defence council meeting with ministers and the main authorities in these matters, said the spokesperson.
The president had indicated hours before the Nice attack that the state of emergency declared immediately after the terrorist attacks in Paris on November 13, 2015 would be lifted on July 26.
Interior Minister Bernard Cazeneuve has arrived in Nice after the attack, said Pierre-Henry Brandet, the spokesperson of Interior Ministry, adding there was no hostage in the incident.
Meanwhile, US president Barack Obama said in a statement that "we have offered any assistance that they may need to investigate this attack and bring those responsible to justice".
"We stand in solidarity and partnership with France, our oldest ally, as they respond to and recover from this attack," Obama added.
The US president also showed his admiration for "the extraordinary resilience and democratic values that have made France an inspiration to the entire world" and he is convinced that this character will "endure long after this devastating and tragic loss of life."