The quake was at a depth of 10 kms (6.21 miles). It was followed by a magnitude 5.4 aftershock 20 minutes later.
The U.S. Tsunami Warning System said there is a tsunami threat following the initial earthquake.
New Zealand's National Emergency Management Agency (NEMA) said it's assessing whether there is a tsunami risk but urged anyone near the coast who felt "a long or strong quake" to get to the nearest high ground immediately.
