A woman cries and asks for her son as she walks near the scene of the attack on Friday. [Photo/Agencies]

Nation 'at war', French PM says following attack in Nice

European governments moved to tighten security on Friday in the wake of a truck terror attack the night before in the southern French city of Nice that killed at least 84 people and critically injured 50.

Security officials warned of the possibility of a second "lone wolf attack".

Men, women and children were in the crowd when a white, 20-ton panel truck zigzagged through the crowd at high speed on the Promenade des Anglais as they watched a fireworks display celebrating Bastille Day, which is France's National Day.

Police shot and killed the driver.

French President Francois Hollande immediately labeled the incident a terror attack.

Prime Minister Manuel Valls told reporters: "We are at war." Three days of national mourning were declared by the government.

The driver was identified as a 31-year-old French-Tunisian. The BBC said his name was Mohamed Lahouaiej Bouhlel and that he was a Nice resident. There were unconfirmed reports that two other suspects were at large.

Police in Nice said the driver, who was known for petty criminal offences, had started his journey in the mountains behind Nice.

Guns and a grenade were found in the vehicle. Eyewitnesses said the driver pulled out a handgun and was exchanging gunfire with police before he was killed.

Germany immediately tightened security along its borders with France. Both countries are part of the Schengen Area, which constitutes European countries that have agreed to abolish passport and customs controls among one another.