A strong 6.0 earthquake felt across the South Island, and as far as Auckland, was not in the Alpine Fault, a seismologist has confirmed.

The quake was centred 45 kilometres north of Geraldine, in South Canterbury, and 10km deep.

It struck at 9.14am.

There were no immediate reports of damage.

GNS seismologist John Ristau says the epicentre was almost exactly in the middle of the island. It's not clear yet which fault was triggered but it occurred 100km east of the Alpine Fault line and is not expected to have any impact on it.

In Geraldine, community board deputy chairperson Janene Adams says her office was rocking and swaying as the quake went on for a "wee while", but she has heard no reports of damage or injuries.

Resident Jeremy Barnes says he had not felt an earthquake that strong since the devastating Christchurch quake in 2011 which he felt in Timaru.

More than 14,000 people have reported feeling the earthquake through the government's Geonet website.

The reports came from throughout the South Island with a few as far afield as Auckland.

Geonet's earlier preliminary assessments of the quake's strength were between 5.9 and 6.4 magnitude.

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