At least 84 people, including several children, have died after a terrorist drove a truck through crowds celebrating Bastille Day in Nice.

Eyewitnesses said the killer swerved from side to side to kill as many people as possible as he drove for hundreds of metres along the Promenade des Anglais on the seafront of the city in the south of France.

At first horrified onlookers assumed the driver had lost control.

But one witness said he then produced a gun before being shot by police.

As sun rose this morning, the lorry could still be seen where it finally came to a halt, its windscreen peppered with bullet holes.

As French President Francois Hollande said the country's state of emergency would be extended for another three months.

Mr Hollande led a wave of condemnation from world leaders, saying: "France has been hit by a tragedy once again.

"This monstrosity of using a lorry to deliberately kill people, many people, who only came out to celebrate their national day.

"France is in tears. It is hurting but it is strong, and she will be strong, always stronger than the fanatics who wish to hurt us."

He also said a military operation was in place which would allow the mobilisation of 10,000 troops and that police from across the country would be called to assist their colleagues in Nice.

Pictures and video footage on social media showed crowds fleeing in terror from the scene on the Promenade des Anglais, which was busy with revellers celebrating and watching fireworks.

Eyewitnesses reported hearing gunshots, and pictures on social media showed armed police with weapons trained on the white lorry.

France is still on alert after the Paris terror attacks on November 13, in which 130 people were killed at sites including the Bataclan Theatre and Stade de France.

The state of emergency initiated after those attacks, which has now been extended, was due to be lifted later this month.

Many families with children had gone to the seafront to watch the Bastille Day fireworks and in the aftermath adults were seen trying to comfort and calm terrified youngsters.

New Foreign Secretary Boris Johnson tweeted that he was "shocked and saddened by the appalling events in Nice, and the terrible loss of life".

A Rihanna concert scheduled for Friday night at the Allianz Riviera stadium in Nice has been cancelled, as have the city's jazz festival, which was due to run from Saturday to Wednesday, and some of the Bastille celebrations over the weekend.