Ten earthquakes measuring more than magnitude 4.9 have been recorded in the Kermadec region north of New Zealand in the past 24 hours.
The largest was a magnitude 6.4 quake.
GeoNet said it has been monitoring what it calls an active sequence in the region.
The quakes have been largely unfelt and have not posed a threat to New Zealand.
It said the sequence was considered to be heightened activity for the region, and was not uncommon and did not mean there was a bigger quake coming.
"There is an active plate boundary in this region (extending up from the Hikurangi Subduction Zone in [New Zealand] up towards Tonga), that has the potential to cause earthquakes large enough to produce tsunami."
GeoNet warned large earthquakes could occur at any time in seismically-active zones.