The officer then seized a civilian car to pursue the young man.
Dozens of police and the Eagle helicopter joined the hunt, scouring the town and surrounding district until the stolen car was found.
"A police-issue firearm was secured in the car at the time the car was stolen, and was still secured in the car when it was recovered last night," McGregor said.
The search is believed to have been hampered by the fact the offender had access to police radio in the car and could potentially listen in to police communications.
McGregor said a review of the theft and the subsequent response, will take place.
"We are very focused on understanding exactly how it occurred and any lessons which can be learned from it."
Anyone with any information about Emery is asked to call Rotorua Police on (07) 3499 400 or Crimestoppers anonymously on 0800 555 111.