Astronomer dismisses meteor theory for North Canterbury's puzzling boom

The cause of a boom that has shaken houses north of Christchurch twice in one week remains a mystery.

Some residents described on social media hearing a sonic boom-type sound at about 8.30pm on Saturday.

A similar loud bang was reported in North Canterbury last week and police were unable to find the source of it.

Woodend-Sefton Community Board chair Shona Powell said the reports suggested the noise was mainly heard in the town of Sefton.

She said it was incredibly puzzling.

"They said it sounded very much like a massive boom, and I think everybody was a bit taken aback seeing as how we did have one just last week, so it has got people wondering."

Powell said there had been much speculation and one theory was that the sound was caused by a meteor.

"That seems to be the common thought because there's been nothing reported in terms of damage.

"It comes out of nowhere, you hear it, and then there's nothing. It's a mystery at the moment."

Astronomer and former superintendent of the Mt John Observatory Alan Gilmore said it was unlikely that a meteor, or anything astronomical, was the cause of the noise.

He said a meteor causing a boom heard on the ground might occur over the whole country once a year.

"Something to make a boom requires a sizeable rock to come down to a low level, closer than 60km from the ground, for the sound to even get to the ground and that's very rare.

"To have the same thing happen in the same place in the country a week apart doesn't sound at all likely. It sounds like there's something else going on in that area to make two booms in one week."