Defence Force explosive training was behind a series of booms that echoed around Auckland, the Defence Force says.
About 4pm yesterday, residents from Piha in the west to Whangaparaoa in the north-east reported being mystified hearing and feeling large thumps, bangs or shocks.
But emergency services received no reports of damage.
Today a Defence Force spokeswoman said its Kaipara Bomb Range was likely to be the source of explosions that were heard.
Several residents sent emails to APNZ saying four or five bangs, sounding like thunder or an earthquake, started about 4pm and continued every quarter of an hour until after 5pm yesterday.
The range was a gazetted high explosive range, where supervised explosive training was carried out regularly, she said.
"Number 5 Squadron was on the range yesterday afternoon conducting trials for the P3K Orion.
"Normally the sound is confined to a 10-15km radius. However, it appears a prevailing westerly wind coupled with low cloud cover have amplified the sound from the explosions," the spokeswoman said.
The trials would be completed by next Wednesday, with four further test days programmed for today, Monday, Tuesday and Wednesday next week.
Several residents sent emails to APNZ today saying four or five bangs, sounding like thunder or an earthquake, started about 4pm and continued every quarter of an hour until after 5pm.
A Fire Service spokesman yesterday said there had been no reports of damage anywhere.
"There's just been mass confusion as to what it was."
GeoNet had also confirmed to the fire service there was no earthquake, he said.
A spokeswoman for the northern communications centre said it had received a handful of calls, "but nobody knows what it is", she said.
WeatherWatch analyst Philip Duncan was supporting the theory of a meteor strike, saying on Twitter the bang came from the sky.
"I felt/heard 2 of the explosions over Auckland earlier - I'm also going with a poss meteor coming in," he said.
Emails from readers today:
• "Heard and felt these in Torbay. Felt the vibration go through my body not just rattling through the house (I'm in an old timber villa nestled into a hill). To me they seemed almost like sonic booms. Something to do with air pressure, rather than something ground-based. Gave me a hell of a fright!" -- Marie Knowles.
• "I live ... on the ridgeline between Albany and Coatesville. I heard four or five bangs/thumps around 4pm yesterday. It felt like something had fallen against the house. As we have scaffolding up at the moment I had to check around the house each time. It sounded like a scaffold board had fallen over or a door had shut (but I was the only one home). The noises were about 15 minutes apart and curious enough to get me up from my computer to tour the property each time. It was very difficult to pinpoint if the noise was coming from inside the house or outside the house. I started to think I had a poltergeist!" -- Heather Carlson.
• "We live in Arkles Bay my House is on Poles, it felt like a Earth Quake as it was Thumping sound like a Sonic Boom it rattled my whole Home. I kept going outside as I thought someone had hit one of those Green Electrical Boxes. Fascinating that no one knows what it was and yet it was felt so widely around Auckland??? Mother Nature?"
• "My neighbour and I at Greenhithe presumed it was from Whenuapai. One of them was big enough to rattle the joinery in my house." -- Lou.
• "It's thunder. Caused by lightning above the clouds. Don't be afraid chicken littles. The sky is not going to fall on your heads ... Well not yesterday any way." -- Peter Griffin
• "I live in Ardmore and about 10 days ago I, my wife and neighbours heard an extremely large bang which set off our three dogs. The power didnt go out, I drove around the rural roads looking for an accident, but nothing. I like the meteor theory as the noise was quite obviously in the sky and echoed like thunder would. We are still mystified." -- Jeremy.
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