The probability of another huge quake over magnitude 7 in the next 24 hours has been put at four per cent - although the likelihood stands at 14 per cent within the next week and 22 per cent across the next 30 days.

Updated aftershock forecasts published by GeoNet this afternoon also show a reduced probability of a 6.0 to 6.9 aftershock quake compared with yesterday.

The probability of one to two happening within the next 24 hours was 37 per cent, there was a 76 per cent chance of up to four in the next seven days, and a 91 per cent chance of up to six in the next 30 days.

Aftershock quakes between 5.0 and 5.9 - a 5.7 quake struck 20km southeast of Seddon and a 5.9 quake hit 30 km north-east of Kaikoura at 2.34pm today - were near certainties.

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According to GeoNet, there was a 99 per cent of an average five of these within 24 hours, 15 within the week and 26 within the next month.

It was "extremely likely" that aftershocks would continue to decrease in frequency over the next 30 days.

"Felt" aftershocks - those greater than magnitude 5 - would occur from the magnitude 7.5 epicentre near Culverden, right up along the Kaikoura coastline to the Cape Palliser and Wellington area.

Dust created by a strong aftershock hangs above the Clarence River north of Kaikoura yesterday. Photo / AP
Dust created by a strong aftershock hangs above the Clarence River north of Kaikoura yesterday. Photo / AP

Within the next 30 days, there was a 15 per cent chance of an earthquake smaller than Monday's main shock, but still measuring between 7.0 and 7.5.

"There are numerous mapped faults in the Marlborough or Cook Strait areas capable of such an earthquake," GeoNet spokesperson Sara McBride said.

"It may also occur on an unmapped fault. This earthquake may be onshore or offshore but close enough to cause severe shaking on land."

This scenario included the possibility of an earthquake in the Hikurangi Subduction Zone, where quakes had the potential to generate a tsunami.

Much less likely - a seven per cent probability within the next 30 days - was of a quake larger than Monday's.

This included the possibility for an earthquake of greater than 8.0, which could be on the plate interface, where the Pacific Plate meets the Australian Plate.

"Although it is still very unlikely, the chances of this occurring have increased since the M7.5 earthquake."

The three scenarios had been developed based on what was know so far, "but be aware that our understanding is evolving as we do more analysis and receive more data".

McBride acknowledged that some of the probabilities were more concerning than others.

"We recognise that while these scenarios may increase anxiety the best thing is to be prepared," she said.

"Remember - if you feel a long or strong earthquake and you are on the coast, evacuate immediately."