RBNZ says earthquake costs are likely to be higher than the $20 billion it estimated before the Christmas Eve aftershocks.

A technical advisory group led by barrister Alan Dormer will report back to government by March 2012 on detailed proposals.

The cost to the crown for the Christchurch earthquakes could rise by another $1 billion, Finance Minister Bill English says.

The government has not ruled out additional future levies if they are needed to rebuild EQC's funds.

Economic and fiscal impacts of the Canterbury earthquakes.