The Otago Corrections Facility near Milton is in lockdown after three staff members were assaulted.

Three prisoners assaulted the staff members at the facility today, said acting prison director Lyndal Miles.

One staff member required further medical treatment for non-life threatening injuries.

Staff followed standard procedures by locking down the site, and the situation is fully under control, she says.

Police have been advised and will investigate.

Violence against staff or other prisoners is not tolerated in prison, Ms Miles says.

Otago Corrections Facility opened in 2007 and accommodates up to 485 male prisoners ranging from low to high-medium security.