Hawke's Bay Regional Prison spent hours in lockdown yesterday after a hoax bomb threat was made - believed to have come from inside the prison.
Police were alerted just before 9.30am yesterday morning about "an item of concern", a spokeswoman said.
Although prison staff were unable to comment, a Corrections spokesman confirmed a bomb threat had been made by telephone.
As police responded to the scene at the prison in Longlands, Hastings, the site went into lockdown. During the morning a white security van blocked the prison entrance and turned cars away.
The lockdown was in place until the early afternoon, with police finishing their investigations just before 2pm, a spokeswoman said.
Corrections confirmed while police were responding to an "item of concern", no item was found, and the prison went "back to normal".
Last night Eastern District Command Centre senior sergeant Dan Foley said they believed the threat had been a hoax, and that the threat had been made by a prisoner.
Police had spoken to a group of inmates yesterday, and were "satisfied" the threat had come from within the prison.
Although yesterday's lockdown and investigation had been "a lot of work" for police, Mr Foley said police were pleased they had been able to identify the threat was a hoax, and that there was no real threat to the prison.