The unexploded bomb was found "in the middle of the tracks" overnight during maintenance work carried out in the area of Saint Denis suburb, the national SNCF rail company said.
The bomb "dated to the Second World War," the RER B suburban train wrote in a post on X.
All traffic to the train station, which hosts Eurostar trains as well as high-speed and local services, was closed as Paris police worked to disable the device.
The Gare du Nord train station lies in the north of Paris and is the country's busiest rail terminal, serving an estimated 700,000 people each day, according to the SNCF.
(with inputs from AFP)
