New Zealand's weather institute said on Friday the weather pattern El Nino had arrived and was expected to lead to high winds, extreme temperature changes and variable rainfall over the coming three months.

Warmer temperatures are likely in the east of both of the country's main islands, New Zealand's National Institute of Water and Atmospheric Research (NIWA) said.

"Spells of unseasonable warmth from Australian air masses will likely be followed up by sharply colder southerlies, with little middle ground," it said in a statement.

Rainfall is most likely to be below normal in the north and east of the North Island and above normal in the west of the South Island, NIWA said.

El Nino could impact milk production and reduce animal growth in New Zealand, which is a major dairy and meat exporter.

The declaration of El Nino follows three consecutive years of La Nina, the counter weather pattern that bought more rain and lower temperatures to the northern and eastern parts of the country and an unprecedented number of tropical and subtropical storms.

Auckland, a city of 1.6 million, was hit by significant flash flooding and landslides in late January that killed four people, damaged roads and destroyed houses. Cyclone Gabrielle hit in February killing 11 people and causing billions of dollars of damage to crops, houses and infrastructure.

Australia declared El Nino had arrived 10 days ago, with the country already experiencing unseasonal heat that led to a total fire ban in Sydney.

NIWA said El Nino was expected to result in normal or above normal fire danger in New Zealand. (Reporting by Lucy Craymer; Editing by Jamie Freed)