After starting in New Zealand's Chatham Islands, the switch-off began for Sydney at 8:30 p.m. local time Saturday and began rolling across the globe, the Australian Broadcasting Corp. reported. It is scheduled to end 24 hours later in Samoa.
The event is designed to boost environmental efforts after the disappointment of December's U.N. talks in Copenhagen, Denmark, which failed to reach an agreement, the report said.
The event is supported by 4,000 cities in a record 125 countries, the report said, and includes 1,200 famous landmarks from the Forbidden City in Beijing to the pyramids in Egypt.
"From Brazil to America, to Canada, all the way down to Australia, Japan and India -- it's a really diverse set of countries taking part this year," Earth Hour executive director Andy Ridley told the broadcaster.
Landmarks scheduled to turn dark included London's Big Ben, Paris's Notre Dame cathedral and the Trevi Fountain in Rome. The report said some U.S. 30 states are on board, and U.S. landmarks scheduled to go dark included Mount Rushmore, San Francisco's Golden Gate Bridge and Chicago's Sears Tower.
In Bangkok, city authorities were told to halt their Earth Hour campaign as anti-government protesters held another major rally, the ABC said.
Earth Hour started in 2007 in Sydney, and this even users of Twitter and Facebook can show their support with special applications that turn their displays dark, the Australian broadcaster said.