A performance of Gustav Holst's <i>The Planets</i> by the Sydney Symphony Orchestra at the Sydney Opera House on Saturday evening was the first major event to mark the ninth annual global Earth Hour to highlight climate change.
The event was streamed live over the internet via the Earth Hour website and people were invited to film themselves performing along with the orchestra and upload it to the site.
The Sydney Opera House switched off its external lights during the hour.
Samoa was the first location to mark Earth Hour, in which participants turn off all the lights in their homes for 60 minutes between 8.30 and 9.30pm local time. People in Fiji and Japan also marked the event.
Hundreds of millions of people worldwide were expected to take part in the event organised by the World Wide Fund for Nature (WWF).
Earth Hour 2007 in Australia with 2.2 million people taking part, and since then the event has grown exponentially into what WWF calls "the world's largest grassroots movement".
In 2014, hundreds of millions of people in 162 countries took part in Earth Hour, according to a report from WWF. The term Earth Hour — and the eponymous hashtag — was mentioned 1.2 billion times on Twitter.
Each year, participants turn off all the lights in their homes for one hour between 8.30 and 9.30pm local time. WWF describes this as "the symbolic act of lights off around the world to inspire and unite people behind a common purpose".
More than 1,200 landmarks — including the Eiffel Tower, Golden Gate Bridge and the Acropolis in Athens — will participate, the WWF said.
The event also aims to raise money for environmental projects as well as awareness about the threat of climate change. In 2014, WWF Singapore's Stop The Killing project raised US$21,346 "to combat wildlife crime in Southeast Asia".
Other projects in 2014 included one by WWF India to help reduce energy use and the carbon footprint of 15,000 schools, and 17 million trees were planted in Kazakhstan.
This year, Earth Hour-related action includes a 100,000-name petition against oil exploration in the Russian Arctic and a project to reduce the use of firewood in Uganda. There are also crowd-funded climate-resilience projects happening in India, Indonesia, Colombia and Portugal.
Ambassadors for the event include UN Secretary General Ban Ki-Moon, South African Archbishop Desmond Tutu and global celebrities like British singer Chris Martin, Italian designer Giorgio Armani, US actor Edward Norton and Taiwanese singer, dancer and actress Jolin Tsai.