The station, which is the busiest in Europe, has been evacuated as authorities attempt to deal with the situation.
Images on social media show armed officers positioned outside the station amid reports of a huge police presence inside the terminal.
Police have confirmed that a security operation is underway and have urged people to follow the instructions of the authorities.
Metro entrances around the station have been closed amid unconfirmed reports of an armed man inside the terminal.
Some people on social media have claimed they were forced to wait on trains when they arrived at Gare du Nord after a security operation was launched just before midnight.
The police headquarters in Paris said the security operation was launched to “dispel any doubt” about a threat.
More to follow…