The starting point is that in the absence of an express provision in the lease for abatement of rent, the Courts will not imply one. The law does not permit an adjustment of a contractual liability to pay rent simply because it is fair to do so.
Whether an express abatement clause will apply to the current circumstances will depend on the wording of the particular clause.
Many commercial leases will be on the current (sixth) edition of the Auckland District Law Society (ADLS) form of lease. Subclause 27.5 of that form of lease provides that if there is an emergency and the Tenant is unable to gain access to the premises to “fully conduct the Tenant’s business from the premises” as a result of reasons of safety of the public that may be associated with the emergency, then a fair proportion of the rent and outgoings shall cease to be payable. Emergency will likely include COVID-19.
Note that any lease executed on the ADLS fifth edition (or earlier) form of lease will not contain these provisions.
What is a ‘fair’ rent abatement in these circumstances will need to be assessed on a case by case basis (e.g. can your business still operate/ use the premises etc) – so talk to your landlord in first instance.