Lights started going off around the world on Saturday in a show of support for renewable energy, given added poignancy by Japan's nuclear disaster, which raises doubts about nuclear power as a possible solution.

Landmarks in thousands of cities, from Sydney Harbour Bridge to the world's tallest building, the Burj Khalifa in Dubai, will turn off the power for Earth Hour, the fifth such event promoting a sustainable future for the planet.

"I think it's going to be the biggest one, but would also say it's very much up to the people," Andy Ridley, co-founder of Earth Hour, told Reuters in Sydney. "There is no one telling you that you have to do it."

The World Wide Fund for Nature (WWF) initiative, along with governments, business and individuals, will cross the globe, with the first lights dimmed across Fiji and New Zealand at 8.30pm (0730 GMT), to lights being turned on again in Samoa 24 hours later.

Some promoting sustainable energy have seen nuclear power as a solution. But the March 11 earthquake and tsunami that crippled the Fukushima Daiichi nuclear plant in northeastern Japan, sending radioactive material into the atmosphere, have made many think twice.

"We did hesitate a bit (about calling for Earth Hour in Japan) because there are many without electricity in disaster-hit areas," said Naoyuki Yamagishi, climate change programme leader for WWF in Japan.

"But we thought by calling out for energy conservation nationwide it would actually boost support for those living in evacuation shelters. While not everyone participating in Earth Hour may oppose nuclear energy, I think this incident has prompted some to reflect on their stances on energy."

In Taiwan, lights went out on the Taipei 101 skyscraper while residents in one area of the city spent the hour of darkness praying for victims of the Japanese disaster.

As for India, a message posted on Twitter said: "In India, thousands of villages experience Earth Hour each hour of the day."

In the Philippines, bells pealed in Catholic churches and fire engines and police cars sounded their sirens.

Australian Prime Minister Julia Gillard lent her voice to Earth Hour by vowing that she and her government would go beyond the hour by "doing everything in my power to deliver a carbon price", a scheme to encourage companies to minimise emissions.

Australia, a leading coal exporter, accounts for about 1.5 per cent of global emissions but is one of the highest per-capita polluters in the developed world due to a reliance on coal-fired power for 80 percent of domestic electricity.

Although Earth Hour kicked off in Fiji, organisers did not have it all their own way in the rugby-crazy country. Lights were switched off but not television, due to the Hong Kong Sevens tournament.

China, the world's top energy consumer and greenhouse gas emitter, turned off the lights at the Bird's Nest Stadium and other Beijing landmarks.

Missing the point slightly, officials left lights running later than usual at one section of the Great Wall so they could be turned off at the allotted time.-Reuters