During an inspection of the HP-3789 vessel, authorities found 10 crew members on board. Four cargo compartments in front of the cabin contained a large quantity of black liquid.
The crew initially told authorities that the substance was fuel oil, or FO, with a total volume of about 70 tonnes.
The vessel was also carrying 41 containers of paint and hardener labelled as originating from Malaysia, Indonesia and China.
The vessel operator and crew members of the HP-3789 could not produce invoices or other documents proving the origin of the goods. They said the entire consignment had been purchased from a foreign vessel.
Authorities are continuing to verify the case and will take action in accordance with regulations.