The death toll continues to rise from an attack in which a truck rammed into a crowd marking the French national day in Nice, Interior Minister Bernard Cazeneuve said on Friday.

At least 80 people have been killed and 18 remain in "critical condition," said the minister.

President Francois Hollande said the death toll included "several children."

Hollande announced an extension of a state of emergency for three months in the country, where Islamic State gunmen and suicide bombers killed 130 people in Paris about eight months ago.

He said "the terrorist character" of the truck attack cannot be denied.

Anti-terror investigations have started. Identity papers of a 31-year-old Franco-Tunisian male, in addition to weapons and grenades, were found in the heavy truck involved, according to reports. The truck driver was shot dead after opening fire at police.

The tragedy took place at the city's famous Promenade des Anglais seafront. The truck ploughed at high speed into spectators watching the fireworks.

Christian Estrosi, president of the region of Provence-Alpes-Cote d'Azur, described on Twitter the incident as "the worst Nice drama in history."

Traffic is closed in Promenade des Anglais, and scheduled cultural events including a jazz festival have been canceled.

European Council President Donald Tusk said the attack was a "tragic paradox." He tweeted a photograph of himself and other European and Asian leaders standing in tribute to the Nice victims at the 11th Asia-Europe Meeting (ASEM) Summit currently held in Ulan Bator, Mongolia.

Chinese Premier Li Keqiang attending the ASEM summit has extended condolences to the victims and their families while condemning "terrorism in all forms."

The United Nations Security Council condemned "in the strongest terms the barbaric and cowardly terrorist attack" which took place in Nice, France.

US President Barack Obama has condemned the attack, saying it "appears to be a horrific terrorist attack" in Nice.