Lights out across Sydney for Earth Hour

The Sydney Opera House and Harbour Bridge have been among the first iconic landmarks across the world to turn their lights out to mark the 10th annual Earth Hour.

The normally luminous structures were plunged into darkness at 8.30 on Saturday night, along with dozens more buildings across the harbour city, as part of the global event designed to highlight the threat of climate change.

Non-essential lights on Melbourne's Bolte Bridge were also switched off, while in Brisbane the Gateway Bridge joined in on the hour of darkness for the event.

More than 350 landmarks across the world including the Eiffel Tower, Empire State Building and Taipei 101 will soon follow suit as Earth Hour sweeps the globe.

Organisers say this year's theme is a celebration of "Places We Love", including beaches, forests, reefs, national parks, mountains, rivers and rural areas, which could be at risk from climate change.

Earth Hour began in Sydney in 2007 and went global the following year, attracting at least 50 million people, organisers say.

This year organisers say events will be held in over 172 countries, with people across the world signalling their support for action on climate change.