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 8:30 pm (0730 GMT), to lights being turned on again in Samoa 24 hours later.

Many promoting sustainable energy have seen nuclear power as a solution. But the March 11 earthquake and tsunami which crippled the Fukushima Daiichi nuclear plant in northeastern Japan sending radioactive material into the atmosphere have made 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.

Engineers were frantically attempting on Saturday to pump out puddles of radioactive water at the plant, which has already sent low levels of radiation into the vegetables and milk near the plant and into dust and tap water in the capital, Tokyo.

The quake and tsunami killed more than 10,000 people and left 17,000 missing and feared dead. Tens of thousands are living in evacuation centres.

One woman who lost her home and a 50-year-old family-owned dress shop to the tsunami was Hiromi Uchikanezaki, 53, of Kirikiri village in Iwate prefecture.

I am living at my brother's house in the hills without electricity or running water, she said when told of Earth Hour. I can feel the support and empathy from people around the world and am grateful.

When asked about the future of nuclear power, she said: It can be a very good thing, but when something like this happens, it is totally terrifying.

In Taiwan, lights will go out on the Taipei 101 skyscraper while residents in one area of the city plan to spend 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.

Australian Prime Minister Julia Gillard lent her voice to Earth Hour by vowing that she and her government will 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 percent 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.

Rugby-crazy Fiji agreed to switch off lights, but not television, due to competition with the ongoing Hong Kong Sevens.