A van ploughed into a crowd leaving a fireworks display in the French Riviera town of Nice on Thursday, injuring several people and sparking panic, in what local officials said could be an attack.

Police and ambulances went to the scene and authorities from the local Alpes-Maritimes prefecture urged residents to stay indoors.

An AFP reporter described seeing a white van driving at high speed onto the famed Promenade des Anglais as people were leaving after the annual Bastille Day celebration display.

"We saw people hit and bits of debris flying around," he said.