The total cost of the Christchurch earthquakes is set to reach about NZ$30 billion ($24.5 billion), much higher than previous estimates, New Zealand's central bank chief said Friday.

Officials have previously put the bill from the quakes that have rocked New Zealand's second city over the past 18 months, including a 6.3-magnitude tremor last February that killed 181 people, at NZ$20 billion.

But Reserve Bank of New Zealand governor Alan Bollard said that only included the cost of reconstructing buildings in the South Island centre, where much of the inner city was destroyed and remains off-limits to the public.

He said the overall bill would approach NZ$30 billion once other factors were factored in, such as insurance claims for lost business, temporary accommodation and claim-handling costs.

"The scale of impacts and ongoing activity means the rebuild is unprecedented," he said in a speech to Christchurch business leaders, noting that reconstructing the city would take at least five years.

Bollard said while "basic repairs" had been carried out, the mammoth rebuilding project had not yet begun in earnest because of the ongoing threat from large aftershocks in the region.

"There have been more than 400 greater than Richter magnitude 4.0, including more than 40 greater than Richter magnitude 5.0 since September 2010, and this has been a shock to everyones hopes for recovery and rebuilding," he said.

The most recent scare occurred when two powerful tremors hit on December 23, sending terrified Christmas shoppers fleeing from stores in panic. Strong aftershock were felt for days afterwards.

As New Zealand prepares to mark the first anniversary of the deadly February 22 quake, Bollard said reconstruction was unlikely to be fully underway until 2013.

He said the New Zealand economy had proved resilient to the impact of the quakes because much of the damage was covered by insurance, unlike other countries such as Japan and China.

In addition, he said once reconstruction was in full swing, the activity it generated was likely to be one of the major drivers for economic growth in New Zealand in coming years.