No-one was injured, and police soon arrived at the boat and arrested four women and five men, police said later that day. They did not say whether the group was armed.
Around 60 passengers were on the ferry travelling down the Elbe river on Thursday afternoon, when a group of PKK supporters came aboard, waving a flag bearing a picture of the head of the movement – Abdullah Öcalan – who is currently serving a lifelong prison sentence in Turkey.
A number of PKK supporters managed to sneak onto the boat without arousing suspicion, and it was only when it was moving did they surround the captain and demand that he not return to the harbour.
Police arrived soon afterwards and pulled up alongside the ferry, enabling the passengers to leave via a walkway between the two boats.
The hijacking is the second in less than seven days, after another group of PKK supporters took charge of a leisure cruiser on the Rhine in Cologne on Sunday.
The pleasure boat was on a tranquil, Sunday afternoon cruise when suddenly half the approximately 20 passengers turned out to be Kurdish activists in disguise and insisted that they read their manifesto, through loudspeakers.
State security officials are investigating Thursday's incident.
The PKK is fighting an armed struggle in eastern Turkey in an attempt to establish an autonomous Kurdistan and greater rights for Kurds in Turkey. It is listed as a terrorist organisation by the US and the European Union.