Aucklanders could be in for a series of moderate earthquakes after two quakes shook the city within five minutes of each other.
The strongest was a magnitude 3.9 located 15 kilometres northeast of the city at 4.05pm on Sunday, which was 6km deep. More than 9000 people reported they had felt the moderate earthquake on the GeoNet Website.
It followed a light quake measuring 3.1 on the Richter scale at 4pm, which was 4km deep and reportedly felt by more than 1000 people.
GNS science duty seismologist Caroline Holden said the pattern of the quakes happening very close geographically and within five minutes of each other was such that it could be a swarm, which was common in the North Island.
"But so far in the last hour we haven't seen any more, so maybe that's it ... but at the moment we're not sure."
A large earthquake was "unlikely" because the region did not have large faultiness, she said.
"But as we've seen ... very small sized earthquakes can get quite a strong shake for Auckland, so we'll have to watch out."
The earthquakes were "tiny" on the scale of earthquakes, but they were "quite shallow and very close to populated centres, so they were felt very strongly around Auckland", Ms Holden said.
The earthquake was centred on Motutapu Island, which is next to Rangitoto Island, the last of Auckland volcanoes to erupt 600 years ago.
The earthquakes were not volcanic earthquakes, Ms Holden said.
"They related to fault lines rather than any magma flowing, so at the moment there's no link with any eruption."
The Fire Service says it received calls from people wanting to confirm there had been a quake, but no reports of damage.
It did not recommend people call the service after an earthquake for this reason because it tied up the phone lines.