About 28 prisoners from Hobart's Risdon Prison overpowered a guard just after 10 o'clock this morning and stole his keys to take control of part of the jail.
A tactical response group has been called in to end the stand-off in an accommodation unit where the prisoners are confined, with the rest of the prison locked down.
The state government says the female guard escaped unhurt, that there has been no violence and no hostages have been taken.
Negotiators have been trying to get the prisoners to return to their cells and the tactical response group remains on stand-by.