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A 5.7 magnitude earthquake has shaken the sea floor about 170 kilometres west of Stewart Island tonight.
The tremor struck at 7:02 pm and was at a focal depth of 15 kilometres.
It is the latest in a series of recent quakes in the area.
GeoNet reported that last Thursday the lower South Island was shaken by three earthquakes over magnitude 5.
All were located about 190km south-west of Tuatapere, which is almost the exact location of tonight's event.
The first of the three was a magnitude 5.8 and was felt by more than 500 people across the lower South Island. It was followed by a number of aftershocks ranging from magnitude three to 4.8 - none of which were reported as being felt.
"These earthquakes occurred just south of the aftershock zone of the July 2009 'Dusky Sound' M7.8 earthquake which was located 100 km north-west of Tuatapere,'' reported GeoNet.
It said historically the south-west corner of the South Island has been one of the most seismically active regions in New Zealand.
It's understood a NZDF aircraft and multiple helicopters are involved.