Eighty people have died in the French coastal resort of Nice when a truck ploughed into a crowd during Bastille Day celebrations on Thursday night, media reports said.

In what it has been described by police as a "major criminal attack" amid speculation it may have been a terrorist attack, the driver reportedly drove at high speed along the seafront before running into the crowd. Police shot the driver dead at the scene and local officials have said the truck was found to contain weapons and grenades.

French President Francois Hollande announced he would be extending a state of emergency in the country, which had been due to end on 26th July, for another three months. "In these circumstances, we must show absolute vigilance," he said. He said the attack had come on France's national day - 14th July - "the symbol of freedom".

"France as a whole is under the threat of Islamic terrorism. We have to demonstrate absolute vigilance and show determination that is unfailing," the UK Guardian reported him as saying.

President Hollande will go to Nice on Friday.

The crowd, which witnesses said had numbered in the thousands, had been gathered on the Promenade des Anglais to watch fireworks. Witnesses reported panic as they tried to seek shelter following the attack.

It is believed some foreign nationals are among those killed. Scores more people were injured in the incident.

US President Barack Obama was among world leaders who have condemned what he said "appears to be a horrific terrorist attack". "On this Bastille Day, we are reminded of the extraordinary resilience and democratic values that have made France an inspiration to the entire world."

Australian Prime Minister Malcolm Turnbull described the attack as a "murderous act of terror".

The attack follows a series of terrorist attacks in France in the past 18 months including a series of attacks across Paris last November in which 130 were killed.