More than 3,400 cities worldwide have taken part in Earth Hour, turning off their lights for one hour at 2030 local time in protest against climate change.
New Zealand was one of the first countries to take part. In Wellington, revellers turned the event into a celebration with a candle-lit concert.
People in Fiji marked the 60 minutes of Earth Hour with candles.
The normally glittering Bird's Nest stadium in Beijing looked distinctly grey.
Hong Kong's financial district was plunged into near darkness.
Campaigners in Greece and across the world aim to create a huge wave of public pressure to force a new climate change treaty.
And in London, the Houses of Parliament, as well as the London Eye, Canary Wharf, the Gherkin and the BT Tower, switched their lights off.
New York, Toronto, Chicago, San Francisco and Las Vegas were among cities in 35 countries that switched off for an hour but critics have dismissed the event as a gimmick that will have little effect.
Even in glittering Las Vegas, some lights were turned off.