Police were called to reports of a "Kalashnikov" weapon in the city centre but later found the alert was triggered by a child's toy.
ADVERTISEMENTThe centre of Lille was shut down for around an hour on Thursday because of a child playing with a toy gun.
French police were alerted to reports of "a man armed with a Kalashnikov" assault rifle in the city's Euralille district.
Traffic was diverted from the scene and the area near Lille Flandres train station was cordoned off by authorities.
But it was later confirmed that the reports of a Kalashnikov were a false alarm and had instead been a young boy playing with a toy weapon.
Police stated on Twitter that they had completed their operation and traffic had resumed in the area.
Authorities have also denied rumours on social media that any shots had been fired during the operation.