Kaniva News reports the quake had a depth of 16km and it struck 20km southeast of Hanmer Springs.
But the New Zealand Civil Defence has revised the first earthquake to a magnitude 7.5, 15km deep, 15 km north-east of Culverden.
It was strongly felt in Christchurch, Wellington, Taranaki, Hamilton and Auckland.
New Zealand Civil Defence is advising all people in coastal areas of the country to move inland to higher ground after a severe magnitude 7.5 earthquake which struck in the South Island.