Pro-ISIS groups have begun celebrating the Nice massacre which has left at least 77 people dead and more than 50 injured - but the terror group is yet to officially claim responsibility.

Scores of Bastille Day revellers were mown down by a truck after gathering to watch a fireworks display in the French city.

Eyewitnesses say there was an exchange of gunfire in the aftermath of the terror attack before the driver was shot dead. A second suspect is currently on the run according to French authorities.

One French media outlet, weekly news magazine Paris Match, is reporting that ISIS has claimed responsibility but as yet there has been no official confirmation.

However, pro-ISIS channels on the secure messaging app Telegram have been flooded with anti-France images celebrating the attack.

The group have mobilised to threaten France and encouraged the use of the #Nice_Attack hashtag.

Guns and grenades were later said to have been found inside the truck, which mounted the pavement at approximately 40mph and steered directly towards hundreds of people watching a fireworks display.

Anti-terror police swooped in as the city was put on lockdown and residents were warned to stay indoors for their safety.

One witness called Antoine said: 'We were at the Neptune beach and a firework display had just finished. That is when we saw a white lorry. It was going quickly at 60-70 kilometres an hour.' 

The gunman jumped out of the truck after ploughing through the pedestrians and began opening fire, witnesses said. Officials said the driver was shot dead near the scene. 

A second suspect is thought to be on the run.

Eyewitness Wassim Bouhlel said that he saw a truck drive into the crowd and then witnessed the man emerge with a gun and start shooting.

'There was carnage on the road,' Bouhlel said. 'Bodies everywhere.'