NICE: A terrorist gunman killed 84 people and wounded scores when he drove a heavy truck at high speed into a crowd that had watched Bastille Day fireworks in the city of Nice on Thursday, officials said.

A lorry loaded with weapons and hand grenades drove on to a pavement in Nice more than a mile before police shot dead the driver.

The killer was a 31-year-old French citizen born in Tunisia. He was said to be known to police but not on a terror watch list.

French President Francoise Hollande said the attack was undeniably of a terrorist nature, according to a Reuters translation of the president's televised national address at 4 a.m. local time. The act was a "monstrous" one, he said, and the victims included "many children."

As hundreds remain in hospital - including 18 fighting for their lives in intensive care - an investigation was opened to look into "mass murder" and investigators searched the home of the driver in the Abattoirs area of Nice.

As the United Nations issued a statement calling the latest "cowardly and barbaric" act, French Prime Minister Manuel Valls tweeted: "The city of Nice has been hit by terrorism on the day of our national holiday. Immense pain, the country is in mourning. The French will face it."

The French Embassy has lowered its flag out of respect for the 84 victims. The embassy in central London made the symbolic move this morning, hours after a lorry mowed down revellers at Bastille celebrations in Nice.