The national state of emergency declared last Wednesday after the Christchurch earthquake has been extended for a further seven days in New Zealand, Civil Defence Minister John Carter said on Tuesday.

Carter said it ensured co-ordination and co-operation between central and local resources.

"Due to the scale of the disaster the civil defence response is beyond the resources of the local authority," he said in a statement.

The declaration gives civil defence emergency management national controller John Hamilton the authority to direct and co- ordinate resources.

The Civil Defence Emergency Management Act requires the declaration to be renewed every seven days.