A man threatening to smash a Corrections worker's head in sparked a lockdown at the Wanganui office.
Brandon Victor Flood was on a community detention sentence when he called the office on September 18 three times.
On the third call he became "displeased" with his "earlier dealings" with another staff member, police prosecutor Sergeant Stephen Butler told Whanganui District Court.
He told the staff member on the phone he was "coming to probation to smash [the other person's] head in".
The office was placed under "lockdown" and police were contacted, though the lockdown happened in the morning before the office was open to the public.
Flood had someone drive him to the probation office and left the scene when he saw police there, Mr Butler said.
He then called the office and gave a false name before asking what was going on.
Flood later handed himself in to police. He said he lost his temper over trying to find out if he had a court date coming up, Mr Butler said.
Flood pleaded guilty to speaking threateningly.
Judge David Cameron convicted him and remanded him to November 19 for sentencing.