The source of booms heard in Whanganui on Wednesday night remain a mystery, but some seismic activity has been recorded around the same time.
A small burst of energy was recorded in Whanganui at the same time the mysterious noises were heard in the region, GNS Science seismologist John Ristau said.
At around 10.15pm "for a few seconds, there was a bit of energy a bit above the background noise levels".
It seemed "more than just a coincidence" the activity took place at the same time people reported hearing the noises in Whanganui, Dr Ristau said.
The activity was not caused by an earthquake, he said, and he was not sure what had caused the noises or the seismic activity.