The "severe quake" which was felt across New Zealand this morning could have been caused by a number of faults, GNS Science says.
The magnitude 7.5 quake centred near Hanmer Springs, struck just after midnight. It was felt across the country and there have been dozens of aftershocks.
GNS duty seismologist Anna Kaiser said it appeared the quake was centred near the Hope fault near Cheviot.
However, there were a number of faultlines in the area and it would take some time for scientists to locate the exact fault.
Ms Kaiser said people should expect the aftershocks to continue.
She said GNS gauges had detected rising sea water levels around Kaikoura, as a result of a tsunami being generated.
She said the quake was "definitely" felt across the country. Most of the aftershocks had been felt in the Kaikoura and Seddon areas.
In a statement GNS said it was a "severe quake".
"This level of shaking includes people experiencing difficulty standing. Furniture and appliances shifting. Substantial damage to fragile or unsecured objects and a few weak buildings may be damaged."