More than 1500 aftershocks have been recorded since the massive magnitude-7.5 earthquake near Hanmer Springs, a few minutes after midnight on Monday.

By 6.50am on Wednesday, GeoNet had recorded 1516 aftershocks.

Between 6pm Tuesday and 6am Wednesday, 328 were recorded, of which 23 were over magnigtude-4.0.

Among the overnight quakes was a magnitude-5.4 quake at 6.09pm and a magnitude-5.8 at 7.30pm. Both were near Kaikoura and at a depth of just 7km.

GeoNet director Dr Ken Gledhill has described the initial earthquake as "a monster quake, one that has shocked us all with its intensity and ferocity".

"Because of its size it made our world shake strongly but relatively slowly for a very long time. It is a complex, brooding beast we are still trying to understand.

"I can't relieve anyone's anxiety about future earthquakes; more will come. What I can say is that preparedness, that old Civil Defence and Emergency Management mantra, is the best solution to being ready for these events."

-Stuff.co.nz