A hijacker claiming to have a bomb has taken at least 20 people hostage on a ferry boat just southwest of the Turkish city of Istanbul.

Turkish media reported that the ferry Kartepe was traveling toward Izmit, when the hijacker seized control of the vessel.

Izmit's mayor, Ibrahim Karaosmanoglu, told local NTV that only one assailant was involved. Earlier reports had said five hijackers were on board.

Details about the incident are still coming in. Turkish news reports say 23 people were on board the vessel.