Residents in coastal areas near the East Cape district are being advised to evacuate
New Zealand's North Island has been shaken by a 7.1 quake, with local reports warning coastal residents to move to higher ground.
The earthquake struck at about 4.40am local time and was centered about 130km northeast of Te Araroa at a depth of about 33km.
The quake was felt as far south as Akaroa - about halfway down the South Island - and as far north as Kerikeri, about 240km north of Auckland.
New Zealand's Ministry of Civil Defence, however, issued a "tsunami potential threat advisory" for all the country's coastal areas.
This was later upgraded to a tsunami warning for the North Island's East Coast, including Auckland, Waikato and Bay of Plenty and the country's upper South Island.
About 90 minutes after the quake, a wave height of 30cm was measured at East Cape, with the New Zealand Ministry of Civil Defence describing this as "the first tsunami activity" and warning that this activity "will continue for several hours".
GNS scientist Anna Keiser told Radio NZ that, although the wave sounded small, it was enough to generate a tsunami.
She added: "At this stage the 30cm is within the marine threat category and people should be vigilant."
Anyone living near the coast in the area has been warned to leave their homes, take their radio with them and immediately go to higher ground.
According to Geonet, which monitors New Zealand's earthquakes, there were 28 aftershocks in the hour following the quake.
Two of these were described as severe - measured at 5.6 and 6.2 on the Richter scale.
No damage has been reported, although power was cut briefly to around 300 homes.
The quake comes a day after a 5.7 tremor nearby, about 62 miles northeast of Te Araroa on the east coast.
New Zealand is on the boundary of the Australian and Pacific tectonic plates and experiences up to 15,000 tremors a year.