A strong aftershock with a magnitude of 6 point 2 shook New Zealand's South Island on Monday, after a 7 point 8-magnitude earthquake rocked the same region earlier on the same day, triggering landslides and a small tsunami.

The quake struck the South Island just after midnight in a mostly rural area. Near the epicentre, it caused fissures in roads and started landslides. Two people were killed. The quake caused damage in the capital Wellington, more than 200 kilometres to the north.

New Zealand's Prime Minister, John Key, visited the affected area, and said the damage bill is likely to be at least "a couple of billion dollars".

Key said, "So some very short-term practical issues that need to be resolved - making sure that we're getting more water, food and ultimately people are here to support the nearly 600 people at the welfare centre because the road access points here are blocked off."

"The only way through is flying people in and out, there's quite a number of tourists now stuck with international connections, so we'll have to think about that."

"There's also the longevity of the businesses here, that short term aren't getting a lot of custom, because again, you know, because there's no access points in and out. That's probably relatively simple compared to the damage of the roads. So the slips are horrendous, and the final point on that, and you have got to believe it's in the billions of dollars to resolve these issues."