Did your phone start going off before the earthquake struck?
The quake occurred at 4:51am on Saturday 25 July, originally measured at a magnitude 5.6 and then upgraded to 5.8 shortly after.
It was centred 5km south-west of Taumarunui, at a depth of just 5km.
On Taranaki Media's Facebook page, people were quick to report the unusual experience of being warned by their phone before feeling a thing, with many questioning where the alert came from and how it works.
The warning was triggered by the Android Earthquake Alerts System.
Google built this feature directly into the Android operating system to give people precious seconds to drop, cover and hold.
Modern Android phones contain tiny accelerometers that can sense movement. When a device is plugged in and stationary, it acts as a mini seismometer.
If the phone detects the initial, fast-moving P-waves of an earthquake, it instantly sends a signal to a central Google server along with a coarse location.
When thousands of phones report this specific movement at the exact same time, the server calculates the epicentre and magnitude of the quake in milliseconds. It then fires an alert to phones in the surrounding areas before the slower, more destructive S-waves arrive.
Because internet data can travel faster than seismic waves, people further away from the epicentre get a larger head start.
If you're on Android and didn't receive the alert, check that location services and earthquake alerts are enabled in your device settings.
Apple iPhone users do not currently have a built-in equivalent for New Zealand, though third-party apps can provide similar notifications.
GeoNet remains the official scientific source for confirmed earthquake data across the country.
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Update: The earthquake has been upgraded to magnitude 5.9, 9km deep, 10km south-west of Taumarunui
