WELLINGTON (Reuters) - Authorities declared an overnight curfew for Saturday after a major earthquake hit New Zealands second biggest city, Christchurch, bringing down power lines and bridges and wrecking roads and building facades. The damages are incredibly frightening. The only thing you can say its a miracle that no one lost their life, Prime Minister John Key told Television NZ after the quake struck with a magnitude of 7.1 from a depth of 10 kms at around 4.35 am local time (5:35 pm British time Friday). He said early estimates for the cost of repairs were around NZ$2 billion (906 million pounds). A curfew was slapped on the central business district of Christchurch between 1900 and 0700 (8:00 am and 8:00 pm British time). Earlier, a formal civil defence state of emergency was imposed in the city of around 350,000 to coordinate recovery operations. The last time authorities declared a local emergency was in late December 2007 when a 6.8 magnitude earthquake hit Gisborne on New Zealands North Island. The earthquake caused damage to some buildings but also caused no casualties. Christchurch city and the neighbouring small towns bore the full force of the quake, which did considerable damage to infrastructure. The damage is immense, its something that has affected every family, every hou-sehold...the hit on our infrastructure, the pipes that deliver the water, the waste water, the bridges, the power supp-lies...has been very significant, Christchurch mayor Bob Parker told reporters. The citys hospital said two men had been admitted with serious injuries, one hit by a falling chimney and the other cut by glass. Police said there were minor instances of looting, which had been quickly contained. In the suburbs many houses had broken windows, toppled chimneys, cracked walls and items thrown off shelves, with some streets and footpaths subsiding.