An 8.8 magnitude earthquake struck off Russia's remote east coast on Wednesday, triggering tsunami waves on multiple countries' shores.
The quake is tied for the sixth-strongest ever recorded, and the strongest since 2011, when a 9.0 magnitude earthquake hit northeast Japan, triggering a devastating tsunami.
Tsunami currents reached parts of New Zealand overnight and the National Emergency Management Agency (NEMA) warned the first surges were unlikely to be the largest.
NEMA had said the threat warning would be in place until midday, but in an update about 12.20pm they said it had been extended to 3pm.
"New Zealand remains under a national strong and unusual current threat.
"This threat level is expected to remain until at least 3pm today. From 3pm, it is possible the threat level will decrease across the west coasts of both the North and South Islands."
NEMA earlier said the threat must be regarded as real until the tsunami alert was cancelled.
NEMA's director Civil Defence Emergency Management John Price told Morning Report the risk was still very high for people thinking of going near the water today.
"We take these matters extremely seriously ... we want them to stay away."
The last thing NEMA wanted was to see anyone harmed.
Evidence of tsunami activity had been seen in North Cape, Tauranga, Kaikōura, Castle Point, and Christchurch and the southern parts of the country.
"This is still an active threat. It is still a threat to human life."
However, there had been a glitch with the alert system which resulted in some people receiving multiple texts, Price said.
There have been two official alerts and NEMA would be trying to work out why some people had received more than that.
Ninety percent of people entering a tsunami wave died, Price said.
"You will see unusually high tidal surges, you'll see unusually high currents and the water level is unpredictable and it's the unpredictability of this that will potentially cause great danger to people."
Various online webcams, dotted along the country's coasts and monitored by RNZ overnight, did not appear to reveal any damage - although daybreak could bring this to light.
Boaties were advised not to remain on their vessels. Auckland Emergency Management opened four Civil Defence Centres for people lived aboard and who did not have friends or family to stay with. The centres would remain open until 8am Thursday.
Auckland Emergency Management said two boaties spent the night at its Waikeke Island civil defence centre.
The Marlborough Harbourmaster has this morning reinstated an order requiring all Cook Strait ferries travelling to Picton to use Marlborough Sound's Northern Entrance.
The ban on the Tory Channel entrance was put in place at 10pm on Wednesday, affecting three sailings overnight and adding 40 minutes to the journey.
It was due to be lifted at 6am today, but an Interislander spokesperson says it will now be reassessed after midday.
A further three sailings are affected.
