Earth Hour, which started in Australia in 2007, is being observed by millions of supporters in 187 countries, who turned off their lights at 8:30 p.m. local time in what organisers describe as the world's "largest grassroots movement for climate change".
"It aims to raise awareness about the importance of protecting the environment and wildlife," Earth Hour organiser WWF Australia chief Dermot O'Gorman told AFP.
"The time for denial is long past. We are losing not only our battle against climate change, but also our battle against the collapse of biodiversity," he said on Twitter.
Images from across Asia showed buildings including Kuala Lumpur's Petronas Towers, as well as the famous harbour skylines of Hong Kong and Singapore, blacking out to mark the occasion.
And in Mexico City major monuments switched off their power including the Angel of Independence, while Colombia's third-largest city Cali saw activists light candles to form the "60+" logo.
"Resources and ecosystems across the world are under assault. Earth hour is an opportunity to show our resolve to change."
The cathedral of Guadalajara is pictured without lights during Earth Hour (AFP)
Threat of extinction
"More than half of plant and animal species face local extinction in some of the world's most naturally rich areas in biodiversity by the turn of this century if we continue along the current path that we are trending in terms of global warming," he said.
The analysis, released last week, said key biodiverse sites around the world projected to be most affected by localised extinction include the Amazon, the world's largest tropical rainforest, and southern Africa's Miombo Woodlands.
While the lights-off event is a symbolic gesture, Earth Hour has led successful campaigns over the past decade to ban plastics in the Galapagos Islands and plant 17 million trees in Kazakhstan.
Sydneysider Dianna Ali, who was having dinner with family as the lights went off in the city, said the initiative had made her more aware of the impact of her lifestyle on the planet's health.
"Since Earth Hour started, it's made me more conscious of how much power I'm using," she told AFP.
"I think... about how much one individual can make a difference."
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
Man Scales Eiffel Tower On Last Day Of Paris Olympics, Arrested: Cops Paris Olympics Winners To Take Home 'Piece Of Eiffel Tower' Olympics 2024: Full List Of Venues At Paris Games Nurse Raped, Killed On Way Home, Body Found 9 Days Later In UP Rahul Gandhi's Seat At Red Fort Triggers Fresh Congress Attack On BJP "Don't Expect Anything From Me": Kolkata Hospital's New Principal Loses Cool Delhi Prisons Announces Remission For 1160 Convicts On Independence Day ISRO To Launch Earth Observation Satellite Tomorrow "Took Advantage Of His Addiction": 5 Charged Over Matthew Perry's Death Track Latest News Live on NDTV.com and get news updates from India and around the world.