Unusual slow-slip seismic movements may mean there's an increased risk of a 7.8 magnitude or greater earthquake in the lower North Island, according to GeoNet.
Simultaneous slips have been recorded at Gisborne, Hawke's Bay and Kapiti, says the earthquake monitoring service on its website on Thursday.
"We've been observing slow-slip events in these regions (and Manawatu) for 15 years now, and we've never seen them happen in multiple locations all at once.
"But we've never tracked slow-slip events after a large magnitude 7.8 earthquake, so this could the normal pattern after such a large quake."
The slow-slip events may mean there's an increased risk of a magnitude 7.8 or greater quake in the lower North Island, GeoNet says.
"Were such a quake to occur it would be likely to cause a large tsunami that would pose a threat to coastal communities in much of the North Island, the upper South Island and Chatham Islands."
GeoNet says that message could be unsettling, and Kiwis must be proactive and prepare for an earthquake and tsunami.
Civil Defence Minister Gerry Brownlee also raised earthquake preparedness in parliament on Thursday, citing the uncertainty slow slips have created about future quakes.
"While it's not scientifically possible to predict future earthquakes, this ongoing seismic activity is a reminder to us all that we live in a seismically active country and should always be prepared for a major earthquake," he said in a statement.
He later criticised parliamentary colleagues who laughed at a question from fellow government MP Chris Bishop about what New Zealanders could do to prepare for a quake.
"It's a good question and it's not a laughing matter in these circumstances. The Kaikoura earthquake has prompted important conversations about being prepared for earthquakes and tsunamis," he said.
New Zealanders should have a household plan, plenty of food, water and other supplies, and if they're near the coast move immediately after a long or strong quake rather than waiting for official warnings.
"The earthquake itself is the natural warning."
The Kaikoura earthquake was a magnitude 7.8 quake in the South Island of New Zealand that occurred two minutes after midnight on November 14.