Traffic ground to a halt at one of France’s busiest train stations on Friday after an unexploded World War II bomb was uncovered just north of Paris, the authorities said.

The bomb was discovered overnight in the Saint-Denis suburb near tracks that lead into the Gare du Nord, a major Parisian transit hub that serves northern France and Europe.

Traffic on high-speed and commuter railways was stopped for hours as the Paris police sent in mine-sweeping crews to clear out the bomb. Eurostar trains, which connect France to Britain, Belgium and the Netherlands, were also disrupted, stranding travelers at the station, which served over 226 million travelers in 2023.

“Trains from and to Gare du Nord are halted until midafternoon at the request of the police,” France’s national railway company said in a travel notice on Friday.

The type of bomb and the circumstances of its discovery were not immediately clear.

Philippe Tabarot, France’s transportation minister, told Sud Radio that there were “no worries” regarding the situation, but that the authorities were taking all necessary precautions to safely remove the bomb.

“Clearing out abandoned luggage happens occasionally, but it’s rather rare for bombs from World War II,” Mr. Tabarot said, adding that he expected train traffic to remain disrupted throughout the day.

It is not uncommon in Europe for construction workers to come across unexploded ordnance from the conflicts that tore the continent apart during the 20th century, but it is rarer to find them in highly populated areas.

Last month, more than 175 practice bombs that had been used for training in the Second World War were found under a children’s playground in northern England. In 2018, thousands of people were evacuated in Berlin after an 1,100-pound World War II-era bomb was uncovered.