Rescuers were monitoring a pod of pilot whales swimming just off the northern tip of New Zealand's South Island late on Tuesday after more than a dozen of the group were killed in a mass stranding.

A State of Emergency was declared in Ngongotaha and the Rotorua Lakes Council was forced to activate its Emergency Operations Centre as wet weather forced evacuations and doused most of the country in large volumes of rain..

The whale stranding was the third largest in New Zealand history, since the country began keeping data in the 1800s.