The Air Force says it is responsible for a mysterious jolt that rippled across large parts of Auckland, alarming many residents.
People thought the noises at about 4pm on Wednesday may have been an earthquake or a meteor.
The Defence Force initially denied involvement, but now admits that its No 5 Squadron was conducting P3K Orion trials which involved dropping bombs at the Kaipara bomb range.
Air Force chief Air Vice Marshall Mike Yardley said people would have heard them conducting annual trials.
He said the sound is normally confined to a 10km to 15km radius, but the westerly wind coupled with low cloud cover amplified the sound.
Air Vice Marshall Yardley said the noises may continue on Thursday and for the first half of next week.