Hundreds of cities and towns in more than 35 nations also went dark, organisers said.

Christchurch in New Zealand was among the first to switch off its lights for an hour from 8pm to 9pm. Suva, Fiji, in the same time zone, also plunged into darkness.

The campaign then moved to Australia - where Sydney's iconic Opera House and Harbour Bridge, as well as shops and homes, blacked out. Next were cities from Asia to Europe, with North America set to follow suit.

'What's amazing is that it's transcending political boundaries and happening in places like China, Vietnam and Papua New Guinea,' said Earth Hour executive director Andy Ridley.

'It really seems to have resonated with everybody.'

Organisers see the event as a way to encourage the world to conserve energy.

Earth Hour debuted last year in Sydney, and a reported two million people and 2,000 businesses participated, organisers said. They said the result was a 10.2percent reduction in the city's greenhouse gas emissions for the hour.

AP