The Empire State Building, the Eiffel Tower, the Kremlin and the L&P bottle, along with a slew of other landmarks around the world, have been darkened to draw attention to climate change.
In a symbolic show of support for the planet, many people across the world switched off their lights for 60 minutes, all at 8.30PM local time.
New Zealand kicked off the event as the lights went out on Auckland's Sky Tower and on the big Lemon & Paeroa bottle in the Waikato town.
In Sydney, a small crowd gathered to see the skyline dim, and Sydney Opera House turn a deep green to symbolise renewable energy.
Ausgrid's Paul Myors says the Sydney electricity network noted a drop in demand in the city's CBD during the event.
"We've see na reduction of around 3 per cent across the Sydney CBD during Earth Hour.
"That's the equivalent of switching off more than half a million energy efficient lightbulbs, and a greenhouse gas reduction of over six tonnes."
Additional reporting: AAP and ARN / Photo: Getty Images