Lights have gone out at famous landmarks across the globe for Earth Hour 2009. Skip related content
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The event, designed to highlight the threat from climate change, saw lights dimmed at the Sydney Opera House and Harbour Bridge, the Eiffel Tower in Paris and London's Houses of Parliament.
Other global landmarks that switched off their lights included the Petronas Towers in Kuala Lumpur, the dome of St Peter's Basilica in Rome, Egypt's Great Pyramids and the Acropolis in Athens.
Conservation group WWF, which started Earth Hour in 2007, was hoping one billion people from nearly 90 countries would take part this year.
The organisers said the action showed millions of people want governments to work out a new UN deal to fight global warming by the end of 2009.
Earth Hour executive director Andy Ridley said: "The primary reason we do it is because we want people to think, even if it is for an hour, what they can do to lower their carbon footprint, and ideally take that beyond the hour."