Earth Hour countdown begins

Australia will tonight lead the world as one of the first nations to observe Earth Hour, the greenhouse awareness initiative born just a year ago in Sydney.

The lights will dim across across the nation's capitals for an hour, and in Melbourne iconic buildings including Flinders Street Station and Federation Square will switch their lights off.

In Sydney it will cast the city's iconic opera house and harbour bridge into darkness.

Earth Hour will be observed around the world at the stroke of 8pm, in each timezone, on March 29.

Only Christchurch in New Zealand and Fiji's Suva were ahead of Australia as the hour rolled around, and more than 30 nations are to follow.

The US cities of San Francisco, Phoenix and Canada's Vancouver will be the final population centres to mark Earth Hour, at 2pm tomorrow Australian-time.

More than 2.2 million Sydneysiders took part in the inaugural Earth Hour, but this year organisers are hoping for a massive and global participation.

"I'm putting my neck on the line but my hope is that we top 100 million people," World Wildlife Fund Australia chief executive Greg Bourne said late today.

"There's 370 cities and municipalities taking part that we know about, and many others as well, so we only need 50 cities of two million people and we'll do it.

"When Canada goes ... tomorrow our time they are estimating some 70 per cent of Canadians will be involved."

Mr Bourne also said Earth Hour, and its images of blacked-out cities, was akin to New Year's Eve as it was celebrated in the world's major cities with fireworks.

"Now we have this image of darkness, and consciousness, going around the world," he said.

"It is a message of hope and optimism ... we the citizens of the world are prepared to take action and we want to defeat climate change."

The core message of Earth Hour is for people to reduce their consumption of electricity, which is usually generated by the burning of fossil fuels.

In Victoria, Flinders Street Station, Federation Square, Eureka Towers Skydeck and the Rialto Towers will be darkened.

A public event will be held at Federation Square, with Victorian Opera, community singers and fire-twirling dancers keeping people entertained.

The Criterion Hotel in the north-central Victorian town of Tatura will also host a pyjama party, with a free beer on offer for those who bring a black balloon along - a symbol of an individual's carbon footprint.

"Pubs do tend to use a fair bit of power and energy," said the pub's licensee Nick Matei.

"We just want to make people more aware, and this is a good point to start."

Many of Brisbane's CBD icons are set to switch off their lights at 8pm, including the Story Bridge and City Hall.

Castlemaine Perkins will for the first time switch off the famous neon lights of its XXXX Man, which stands proudly above its Milton brewery.

In Canberra, more than 100 federal government departments and agencies have signed up to switch off for Earth Hour.

The High Court of Australia, National Library of Australia, Australian War Memorial, Parliament House, National Museum of Australia, National Science and Technology Centre and Royal Australian Mint are among the iconic buildings in Canberra to be switching off their lights.

"Even with a function scheduled on the night, the National Gallery of Australia has signed up to switch off as many lights as possible, to conserve energy for the benefit of our environment," Climate Change Minister Penny Wong said in a statement.

"The Australian government is throwing its full support behind the efforts of WWF in organising Earth Hour."