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France: At least 84 people have been killed in the southern French town of Nice when a truck ran into a crowd celebrating the Bastille Day national holiday.

French daily newspaper Le Figaro quoted a police source as saying 73 people have died. More than 100 have been injured.

The white truck mounted the footpath and drove for "100 metres" at speed into the crowd on the Promenade des Anglais seaside walk in the centre of town on Thursday night, regional newspaper Nice Matin reported.

Bodies were strewn across the road.

Original reports put the death toll at up to 30

DFAT says Australian embassy is working to see if any Australians have been affected.

CNN is now quoting French television network BFMTV, in turn quoting a local police source, as confirming that the driver of the truck has been shot dead.

An eyewitness report said the driver emerged from the truck shooting before being shot and killed himself.

French television channel BFM TV said the local prefecture in Nice was treating the incident as an attack and was asking people to stay at home.

Nice Matin quoted its reporter at the scene saying there were many injured people and blood on the street.

It published a photograph of a damaged, long-distance delivery truck, which it said was "riddled with bullets" and images of emergency services treating the injured.

Damien Allemand, the paper's correspondent, was quoted as saying: "People are running. It's panic. He rode up on to the Prom and piled into the crowd ... There are people covered in blood. There must be many injured."

There were reports of explosions and gunshots as people scrambled to escape.

Almost exactly eight months ago, in November, Islamic State militants killed 130 people on a Friday night in Paris.

There are reports of an exchange of gunfire at the scene as people scrambled to escape.

"Dear Nicois," local government leader Christian Estrosi wrote in a tweet. "The driver of a truck appears to have killed dozens of people. Stay at home for the time being. More news to follow."

The Associated Press quoted a witness describing "bodies everywhere".

Christian Estrosi, the President of the Provence-Alpes Côte d'Azur region warned of a death toll in the "dozens" and told locals in a social media posting to stay inside.

Hali Rose McField a witness told CNN a crowd had gathered on a promenade to watch fireworks to mark France's national day when the truck struck. 

"I saw some parents holding onto their children," Ms McField said. "It was very scary."

American Eric Drattell told the network that helicopters were circling above the scene and said hundreds of people had taken shelter near the beach.

It is close to peak tourist season for the holiday site.

The French President, Francois Hollande, had only hours earlier confirmed that France would not extend a national "state of emergency" brought in after deadly terrorist attacks rocked the French capital last year.

The state of emergency was due to expire on July 26.