That was more than 1.2 degrees Celsius above the long-term average and beat the previous record by 0.2 degrees Celsius.
Chris Brandolino, a principal scientist with the agency, said the high temperatures were driven by a combination of weather cycles including the La Niña system, which brings cooler-than-normal ocean temperatures to the tropical Pacific and warmer air to New Zealand.
He said manmade factors also contributed.
“Climate change continues to influence New Zealand's long-term temperature trend,” Brandolino told reporters.
He said the levels of carbon dioxide measured in the atmosphere near Wellington keep rising.
“Unfortunately you can see that trend, dating back to before 2014, continues to go upward and in the wrong direction,” he said.
Brandolino said there was no discernable effect on last year's weather from the massive eruption of a volcano in Tonga.
He said he expects the first few months of 2023 to continue being warmer and wetter than normal, and for temperatures over time to keep rising.
"It's hard to see us breaking from the trend that we are on," Brandolino said.