The quake had a depth of 33km and was felt by almost 9000 people, mostly on the east coast from Gisborne and Napier to Christchurch, according to GeoNet.
Civil Defence says New Zealand coastal areas may experience strong and unusual currents and unpredictable surges at the shore.
Some people have reported feeling the early morning quake on Twitter:
About an hour before New Zealand's 7.4 shock, a magnitude 5.1 quake struck in Tongan waters, about 100km east north east of the main islands.
-Additonal reporting from RNZ.