The global movement, celebrating its 20th anniversary, encourages nations to turn off their lights for an hour to bring attention to the issues of nature loss and climate change.
Auckland monuments including the Sky Tower and Harbour Bridge, and Wellington's parliament buildings went dark on Saturday night.
Throughout the night other monuments across the globe, including the Empire State Building in New York and the Brandenburg Gate in Berlin, will switch off their lights in solidarity.
WWF Germany's head of climate, Viviane Raddatz, said people care about protecting the environment.
"Currently, the climate crisis is repeatedly pushed into the background in light of the many global challenges. However, it doesn't disappear. On the contrary, it exacerbates many of these crises," she said.
"With Earth Hour, we are bringing climate action back into the public spotlight. We are making it visible. People care about this issue and it belongs at the very top of the political agenda."
Supporters are invited to "give an hour for Earth" by spending 60 minutes doing something positive for the planet.
WWF International said more than three million hours were pledged in 2025, with more than 118 countries and territories joining in.
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