An officer has been punched and had a dog set on him in a violent altercation at a Work and Income office in Foxton, near Levin.
The police say they were called because a 40-year-old man was acting angrily at the office.
An officer pepper-sprayed the man and his dog, but it proved ineffective.
The officer was attacked and brought to the ground, and had to call for back-up.
His attacker fled the scene and was found by police at a home just outside of Foxton.
They say he wielded a metal bar and threatened officers.
The man was confronted with a taser and surrendered.
The officer who was attacked sustained moderate to serious injuries.
Acting Manawatu Area Commander Detective Inspector Chris Bensemann said it was a shocking attack.
"He was confronted by the person. He tried to calm the situation. The person attacked him, and basically called his dog on the police officer and was attacked by the dog and the person simultaneously.
"The dog appears to have made contact with him around the buttocks area at first, and then made his way up his body to his head area," he said.
"We are rallying around our colleague who was simply doing their job when they have been viciously assaulted.
"This appalling and unprovoked attack on this skilled and valued officer shows the volatile nature of our work and how incidents we attend can quickly escalate," he said.
Mr Bensemann said a number of witnesses were being spoken to by police.
The man will face a number of charges and his dog has been seized by local animal control.
The Ministry of Social Development greatly increased security at Work and Income offices after two of its workers were shot dead at work in Ashburton last year.