But the authorities denied any hostages had been taken - though they conceded a struggle had broken out inside Istanbul's high security Metris prison.
All day, police helicopters circled the prison complex as commandos took up position outside. Inside, jailed members of the Islamic Great Eastern Riders Front had apparently rioted at the news some were to go to another prison. The state prosecutor, Celil Demircioglu, sent to take charge, insisted there had been been only "pushing and shoving", and everything was back to normal.
The Front, which supports the introduction of Islamic sharia law in Turkey, and has been blamed for bomb attacks, said they had released all the hostages.
Turkey has an ongoing struggle to wrest back control of its lawless prisons, where inmates have access to mobile phones and guns. Several people - including a prominent mafia leader - were killed in a recent jail gunbattle, and the rebel Kurdistan Workers' Party (PKK) has been known to train its jailed members in prison.
The authorities are trying to take control by moving prisoners from traditional jails where large numbers live in single wards, to new prisons with small cells. There are many jail protests. Political groups have traditionally been housed together in single wards, and object to being broken up.
The prison riots are embarrassing for Turkey at a time when it is hoping to be named as a candidate for membership of the European Union. Usually, Turkish guards are accused of maltreating prisoners.