A tsunami of half a metre has been measured at the Chatham Islands and ten centimetres at East Cape.
The Chatham Island activity was first recorded as 20 centimetres, but has been upgraded to 50 centimetres.
Civil Defence says these are just the first arrivals and larger waves may follow over a period of several hours. It is assuring people it is monitoring the situation closely.
It is continuing to warn historical data suggests waves could reach as high at three metres on the Chatham Islands and Banks Peninsula.
Waves around the rest of the country are expected to be no higher than a metre, but that does not take tides into account. Civil Defence says the greatest waves could occur six to 12 hours after the first wave arrives.
Estimated wave arrival times
Chatham Islands (Kaingaroa) 07.52
Chatham Islands (Waitangi) 07.35
North Cape 09.24
Auckland (North Head) 10.52
Mt Maunganui 09.04
East Cape 08.24
New Plymouth 11.26
Marlborough Sounds (Tory Channel) 09.08
Christchurch (New Brighton) 09.35
Milford Sound 09.35
Stewart Island 09.51
- NEWSTALK ZB