Something I was inspired to look up post a discussion on Facebook...

http://www.legislation.govt.nz/regulation/public/2004/0427/latest/DLM303083.html

Land Transport (Road User) Rule 2004 (SR 2004/427) (as at 01 October 2011)

.1 Drivers must not exceed speed limits

(1) A driver must not drive a vehicle at a speed exceeding the applicable speed limit (being a permanent, variable, holiday, urban, rural, temporary, or other speed limit).

(2) The fact that a vehicle is driven at a speed that does not exceed the applicable speed limit does not excuse an alleged breach of a provision of any other Part of this rule.

(3) A driver who drives at a speed exceeding the applicable speed limit is not in breach of subclause (1) if the driver proves that, at the time the vehicle was being driven,—

(a) the vehicle was being used by an enforcement officer engaged on urgent duty and compliance with the speed limit would be likely to prevent the execution of the officer's duty; or

(b) the vehicle was an emergency vehicle being used in an emergency and was operating a red beacon or a siren, or both; or

(c) the vehicle was being used (on a road subject to a speed limit of 60 km per hour or more) to convey a member of the Executive Council engaged on urgent public business, or to convey any other person authorised for the purpose by the Minister and engaged on urgent public business in the execution of the person's functions.