"There is a good chance that it is something fairly innocuous," a police source said.
A resident raised the alarm at around 10:30 pm and the bomb squad was on site in the suburb of Lambersart as a precaution.
At the end of August, a concert in the Dutch city of Rotterdam was cancelled at the last moment after a tip-off from Spanish police. The driver of a van carrying several gas cylinders near the venue was arrested but later
In June, a major bomb squad operation was launched after a vehicle with a dozen bottles of butane hidden under a tarpaulin was discovered in the Isere department of eastern France. It turned out that the driver was stealing from his employer, a freight company.
France has been under a state of emergency since Islamic State jihadists struck in Paris in November 2015, killing 130 people.
Since that large-scale attack and last year's Nice truck attack that killed 86, France has suffered a string of smaller assaults mainly targeting security forces.