Landmarks like the Supertrees at Gardens by the Bay and the Esplanade went dark for an hour last night.
Dozens of office buildings, hotels and shopping malls also turned off non-essential lighting from 8.30pm to 9.30pm to mark Earth Hour - a global initiative by the World Wildlife Fund to support more sustainable living - in Singapore.
Sydney's skyline was among the first in the world to go dark as the event kicked off. Many of the world's iconic attractions, including the Petronas Towers in Kuala Lumpur, the Bird's Nest in Beijing, and the Burj Khalifa in Dubai took part.
In Japan's north-east, residents lit candles to both show support for the campaign and mourn victims of the 2011 quake-tsunami disaster, organisers said.
At Singapore's Marina Bay floating platform, about 5,000 people gathered from late afternoon and many danced on special energy absorbing pads to generate enough electricity to power an outdoor movie screening.
Acting Minister for Manpower and Senior Minister of State for National Development Tan Chuan- Jin, who spoke at the event, called on all Singaporeans to do their part to save the environment with small, simple acts.
"All these little efforts do count," he said.