Investigations are under way since Friday night to locate a missing passenger from the Blue Star 2 passenger ferry in the western area of the islet Patroclos in the Saronic Gulf.
According to the Port Authority, a witness sailing by saw what he believed to be a man fall into the sea, with wind blowing at 4 Beaufort intensity.
Three coast guard vessels were immediately dispatched to the area, while five additional boats were already in the area. A Navy helicopter was also on its way.
The ship had sailed from Piraeus and its route was Syros - Patmos - Leros - Kalymnos - Kos - Rhodes.