Their attacks include one holdup in which the terrified victim made desperate pleas for help into a live security camera.
Police believe at least two of the four heists in Orewa and Riverhead are connected, and say all could be the work of the same gunman.
Three have happened over the past 11 days.
In one, on Monday last week, a terrified golf instructor tried desperately to get his boss' attention over a live security camera as he was being tied up by the gunman.
The instructor was waiting for a client at the New Sky Driving Range in Riverhead when the gunman came into the store and walked behind the counter.
"He was holding a pistol and cocked it with his left hand. I heard a clicking noise. He was holding the gun near his right hip," the instructor told police.
The robber demanded cash and the instructor emptied the till and gave the man money from his wallet.
He then taped the instructor's hands behind his back.
"While I was being taped up, I started making faces towards the security camera in the shop. The security cameras in the shop are linked to the owner's house, which is next door to the driving range. I made the faces in case someone was working so they would know that I was in trouble."
The gunman pushed the instructor to the ground and told him to stay put. He stole a bag of golf clubs worth about $1800 as he left.
The next day, a 20-year-old was in his car at McDonald's in Orewa using his iPad when a Maori youth aged about 17 with a goatee, and a scar on his right cheek, got into the passenger seat.
He said, "That's a nice iPad", and pointed a pistol at the man.
"I pushed it away, trying to twist the gun at the same time," the man told police. "I twisted the gun. It was then facing the front windscreen of my vehicle.
"I opened the door while holding on to the pistol and jumped out of my vehicle, hoping he would realise that he is in a public place with cameras and witnesses."
The young robber then put the pistol under his blue hooded jumper and continued pointing it at the man.
"I stated that it wasn't a real gun. He asked how I knew this and I said, 'You would have shot me by now'."
The robber got into a white Toyota Hiace van - which had stolen licence plates and had been used in several drive-off petrol thefts just before the incident - and left with three others.
The same McDonald's was hit again this week, when a man walked into the restaurant, pointed a pistol at staff behind the counter and told them to get face-down on the floor.
He made the manager lead him to the store's safe, and kept the gun pointed at her while she put an undisclosed amount of cash into a yellow plastic shopping bag.
He then left through a back door.
Police dog handlers tracked him but lost his scent in a nearby dead-end street. They believe he had a car waiting there.
Police are also investigating a robbery at the Hallertau restaurant and bar in Riverhead on April 11.
The manager was counting the daily takings in the office when a man burst into the room and pointed a pistol at her.
"Don't make a fuss out of this. I have been watching from outside. I know you know the safe code - now open it," he said to her.
He took $1000 and fled.
Detective Nick Poland, of Rodney police, said the spate of pistol crime was a serious concern.
"Four jobs in the Rodney area involving firearms in three weeks - it's unusual."
He said the two incidents in Riverhead appeared to be connected, as were the two in Orewa. It was possible all four were linked.
* Anyone with information on any of the incidents should contact Detective John Gilbert at Orewa on (09) 427-4532.
THE HOLDUPS
April 11: Gunman robs Hallertau restaurant and bar on the Coatesville-Riverhead highway.
April 25: Gunman tapes golf instructor's hands and robs the New Sky Driving Range, also on the Coatesville-Riverhead highway. Victim tries to attract attention of owner over security camera.
April 26: Man has pistol held to his neck as he sits in a car at McDonald's in Orewa.
May 2: A man with a pistol robs the same McDonald's, forcing staff to the floor and taking cash in a yellow shopping bag.
