Australia's Sydney Harbor went dark as lights were turned off at the iconic Sydney Opera House and Harbor Bridge as part of Earth Hour, a global event calling attention to climate change.
First organized in Sydney in 2007, at least 3,929 communities around the world are shutting off lights this year in the event rolling through the world's time zones.
Hundreds of landmarks around the world are expected to go dark for an hour as nightfall circles the globe Saturday night.
This year's Earth Hour officially started in the remote Chatham Island chain about 800 kilometers southeast of New Zealand.
Organizers hope up to a billion people from small villages in Namibia to sprawling cities in Asia will participate in an international effort to cut greenhouse gas emissions, which many scientists blame for a warming climate.
Some information for this report was provided by AFP, AP and Reuters.