The magnitude 6 earthquake that hit the New Zealand city of Christchurch on Monday could cost insurers between US$3bn and US$5bn, according to risk modelling firm EQECAT.

The epicentre of the quake was six miles to the south-east of Christchurch's central business district, which had already been ravaged by a magnitude 6.1 earthquake on February 21 earthquake and hit to a lesser extent by the more distant magnitude 7 event on 3 September 2010.

EQECAT said the latest quake is not expected to cause significant damage to buildings undamaged by the February event, but will cause incremental damage and loss.

The firm added that had the quake hit directly after the February event, it would have caused additional losses of between US$1bn and US$2bn. However, four months on, EQECAT estimates the damage will cost insurers between US$3bn and US$5bn, with the incremental losses occuring to repaired structures and facilities.

EQCAT estimates that the September 2010 earthquake cost insurers between US$4bn and US$6bn, while the February 2011 quake cost between US$8bn and US$12bn.