THE New Zealand government and private insurers are facing a tough round of negotiations over whether Christchurch's deadly earthquake was an aftershock from the bigger, but less damaging, quake that shook the region last September.

While the outcome will make little difference for those directly affected by Tuesday's earthquake, it could determine who will shoulder the bulk of insurance payments.

A giant boulder crashed through a house during Tuesday's earthquake near Lyttelton, on the outskirts of Christchurch. Credit:AP

With forecasts that the total cost could top $12 billion, insurance executives from Suncorp, one of Australia's biggest insurers, yesterday said the market for earthquake cover was likely to be ''changed forever''.

This suggests future earthquake coverage could be limited, or even impossible to get in some parts of the world.