The captain of the Dongwon-ho was contacted by radio at around 3 AM on Friday, and all the crew has been confirmed to be safe, the South Korean Yonhap News Agency said on Saturday.
US$ 400.000 ransom for releasing sailors.
Armed elements seizing the vessel asked to be paid a US$ 400.000 ransom for releasing the hostages, according to AFP.
AFP said that the kidnappers called to AFP Representative Office in Somali capital, Mogadishu, and laid down the condition. The call was carried out in habour city of Obbia where the kidnapped vessel is believed to anchor.
The ship's owner, Busan-based Dongwon Fisheries Co., has made two rounds of negotiations with the hijackers, but little progress was made.
Five Vietnamese sailors include Nguyen Van Hoi (1976), Tran Xuan Luan (1974), Nguyen Trinh Tho (1980), Hoang Dinh Tai (1984), Nguyen Xuan Qua (1976).