A 5.6 magnitude quake hit 40 km west of Milford Sound just before 10pm today.
GeoNet said it was 5km deep and was reported as being felt by more than 2000 people.
It was followed seven minutes later by a magnitude 4 quake, at a depth of 5km, in the same area.
The second shake was initially reported as magnitude 3.5 and later revised.