Whangarei Sergeant Paul Nicholas said they arrested a 42-year-old man as he tried to leave the house. The specialist Armed Offenders Squad had been called but the arrest was made before they arrived.
However, officers searched the property and found the imitation firearm in the house.
Mr Nicholas said the firearm was a fake Walther P99 and could be bought at sports shops.
It was extremely difficult to tell it apart from the real thing.
He said the imitation was an excellent replica and was capable of firing plastic pellets.
"If you had it pointed at you, you would think it was the real thing.
"If someone presented it at a police officer they would be shot," Mr Nicholas said.
"An officer can't stand around and second guess if it's a toy gun. They are putting themselves and police at risk.
"It's common sense you don't point guns at people."
The imitation was even stamped with Walther P99 and it was only on very close up inspection "Made in Korea" could be seen.
The Otangarei man is now facing a charge of carrying an imitation firearm, which carries a maximum penalty of two years in jail.
He also faces another charge of presenting a firearm which is punishable by a maximum three-month jail term.
He was released on police bail and will appear in the Whangarei District Court today.
Last week a man in Raumanga sparked an Armed Offenders Squad call-out after he was seen running around with an imitation gun that looked strikingly like a sawn-off shotgun.
He was not charged.
