The rupture stretched from Haupiri River on the West Coast of the South Island down at least as far as Milford Sound and the two researchers estimate it reached a magnitude of 8.1, higher than the previously thought mean magnitude of 7.9.

Christchurch was rattled by a magnitude 4.0 earthquake this morning.

A "sudden rise" in volcanic activity at Mt Tongariro has prompted scientists to lift its volcanic alert status for the first time. But local businesses and conservation authorities remain unconcerned.