At least two children died and about 50 were hospitalised on Friday after a man smashed a truck into a crowd in the French Riviera city of Nice.

Two children died during surgery at a paediatric hospital close the scene of the attack, and others were "hanging between life and death," a hospital official said.

Around 50 children were being treated, the official said. Many families were among the revellers who attended the fireworks display for France's July 14 national holiday.