Turkish commandos killed a lone hijacker, identified as a Kurdish militant armed with a bomb, in a pre-dawn operation to rescue more than 20 passengers and crew held hostage for 12 hours on a high-speed ferry near Istanbul.

Hostages aboard the 'Kartepe' ferry later described how the hijacker was shot dead minutes after the commandos slipped aboard.

None of the 18 passengers or six crew were hurt, but some were taken to a hospital for checks after their ordeal.

The Interior Minister identified the dead hijacker as Mensur Guzel, saying he was a member of the militant Kurdistan Workers Party (PKK).

Officials had described the man as carrying a device with cables with a switch. Before the minister confirmed explosives were found, the provincial governor of Kocaeli had said it was a fake bomb.

Coastguard vessels with commandos aboard had tracked the "sea bus" in the Sea of Marmara before it ran low on fuel and dropped anchor.

Shortly before 5am a flurry of activity was evident on the ferry's main deck. Hazy television pictures showed figures moving in the aisle between rows of empty seats. A few people were apparently wearing life jackets.

Orders were given for marine commandos to storm the ferry at 5.35am as it lay anchored off shore.

Passengers became alarmed the ferry was taking too long for the short run between the towns of Izmit and Karamursel and was off course, but only realised it had been hijacked when they saw news reports on the television in the passenger lounge.

Earlier reports said up to five suspected Kurdish militants armed with explosives carried out the hijacking on the high-speed ferry.

There was no immediate comment from the PKK, which is listed as a terrorist organisation by Turkey, the U.S. and the European Union, RTE reported.