If the amount of cannabis is confirmed then it would be one of the largest quantities of drugs found by the Greek Coast Guard.
The vessel, a tugboat, was under surveillance in the last 48 hours. According to initial information, it set sail from Nicosia on November 30 with Malta as destination.
The vessel has been escorted to the port of Aghia Galini and the six members of the crew have been arrested.
The Coast Guard will make official announcements after the final weighing of the cannabis.