"We can confirm that a notification has been received. The investigation is now in the hands of the federal police," a port administration official was quoted as saying by the news agency on Monday.
The vessel had to anchor in the North Sea and was forbidden from entering the port until the inspection was completed, Belga reported.
Reports suggest the explosive device could possibly be planted in a car on board the ship and could detonate after it entered the port. The police cannot rule out that drug traffickers, who actively use the port of Antwerp for smuggling, might be involved in the incident.