Commandos stormed the ferry at dawn and killed the hijacker, media reports and hostage accounts said.

"We saw the commandos (boarding). They finished it in 10 minutes," former hostage Ceyhun Tezel told the NTV news channel. "We didn't see them (killing the hijacker), but we heard three shots first, and then three more," he said, adding: "We prayed and thanked to God that we survived."

Istanbul Governor Huseyin Avni Mutlu said the hijacker, aged about 30, was a member of the banned Kurdistan Workers' Party (PKK). "Soon after the beginning of an operation, the hijacker was captured dead," he said.

Kocaeli governor Ercan Topaca said the hijacker, reportedly seeking media attention, had been carrying a "mechanism" that looked like a bomb.

"No bomb was found on the (hijacker's) body," the Anatolia news agency quoted Topaca as saying. "A mechanism made of bottles and wires, which was designed to look like a bomb, was found," he said.

NTV said police raided the house of the hijacker in city of Izmit and obtained documents, while Topaca said one person was arrested in Izmit in connection with the hikacking.

The ferry Kartepe was hijacked around 1600 GMT Friday in the Sea of Marmara, where PKK leader Abdullah Ocalan is jailed on an island.

"We should have arrived at the destination point in 20 minutes. When we were delayed and saw that the (ferry) was going somewhere else, we understood that we were being hijacked," Tezel said.

The former hostage said the passengers did not see the hijacker because he was on the upper deck and they were below.

Transport Minister Binali Yildirim earlier spoke of four or five hijackers, but Mutlu said there was only one.

All the passengers and crew were safe, Mutlu added, as television footage showed them being evacuated with boats. Then they were sent to police station to testify, media reports said.

Security forces under the command of Interior Minister Idris Naim Sahin boarded the ferry off the coast of Silivri, a town west of Istanbul, around 0335 GMT on Saturday.

Yildirim said 18 passengers including five women, four crew and two trainees were aboard the vessel, which was plying its normal route in the north of the Sea of Marmara when it was seized.

The boat was anchored off Silivri, after sailing in circles until it ran out of gas, Dogan news agency reported.

The hijacker told the ferry's captain that he wanted media publicity, mayor Ismail Karaosmanoglu told NTV. Yildirim added that the attacker had conveyed demands for food and fuel through the captured captain.

Nearby boat and ferry trips between Istanbul and Yalova, about one hour apart, were cancelled after the attack, media reports said.

The island of Imrali, where Ocalan, the jailed PKK leader, is held, is about 120 kilometres (75 miles) southwest of the hijacking spot. Turkish media say the hijacker was assumed to be heading for the island.

"Measures were boosted around the island of Imrali where PKK leader Abdullah Ocalan, who has not been allowed to meet with his lawyers for months, is being held," said the pro-Kurdish Firat news agency.

Patrol boats had been deployed and kept watch in a five nautical mile no-go area around the island, it added.

Pro-Kurdish demonstrations are regularly held in Turkish cities in support of Ocalan, who is still considered the PKK's chief despite his imprisonment.

The PKK, listed as a terrorist organisation by Turkey and much of the international community, took up arms for Kurdish independence in southeastern Turkey in 1984, sparking a conflict that has claimed some 45,000 lives.

Clashes between the PKK and the army have escalated since mid-2011.

A surge of attacks by PKK rebels also caused civilian deaths in Turkey, prompting the Turkish military to launch in October a cross-border operation against rebel hideouts in northern Iraq.