The explosion was heard in the Canterbury town of Woodend. Photo: CC 2.0 BY-SA / Gavin Treadgold
Police have been unable to identify the source of a mystery boom that shook houses north of Christchurch.
Police said several members of the public heard a boom shortly before 9am today. Officers on patrol in Woodend also reported hearing it.
Woodend-Sefton Community Board chair Shona Powell said she wondered if it was the sound of a car backfiring.
"It came out of nowhere, a loud bang, and then there was nothing afterwards. So it came and went extremely quickly.
"Then, as you do, you go on to social media and find it's rather more widespread."
People have described a sonic boom-type sound on social media, with one person saying it sounded like a bomb dropping.