Thousands of people across the capital are preparing to turn off the lights Saturday during the third annual Earth Hour.

Ottawa is one of more than 2,850 communities worldwide that will darken its buildings and shut down power for a single hour starting at 8:30 p.m.

Hydro Ottawa hopes to improve on the four-per-cent drop in power consumption during last year's Earth Hour.

Organizers hope one billion people participate worldwide, a 20-fold increase from 2008.

Keith Stewart of World Wildlife Fund-Canada says a recent poll found more than 80 per cent of Canadians said they were going to be participating in Earth Hour.

He says this year's Earth Hour is more important than ever, since a successor to the Kyoto Accord is being negotiated this year.

Earth Hour passes through Far East

Revelers in Australia attended candlelit speed-dating events and watched outdoor concerts Saturday. Lights in Sydney Harbour dimmed, which left shadows dancing across the iconic Harbour Bridge and Opera House.

On the Chatham Islands, which are about 800 kilometres east of New Zealand, officials kicked off Earth Hour by turning off all diesel generators. The lights on Auckland's Sky Tower, the tallest man-made structure in New Zealand, shut off not long afterward.

About 44 cities and towns in New Zealand dimmed their lights, and more than 60,000 people attended an Earth Hour-themed hot air balloon festival in the city of Hamilton.

The country's 26-member winter staff team at Scott Base in Antarctica powered down to minimum safety lighting and switched off appliances and computers.

In China, residents participated in Earth Hour for the first time. Lights were turned off at Beijing's popular Olympic venues, such as the Bird's Nest Stadium and Water Cube.

Shanghai planned to cut lights in government buildings and along the city's waterfront. Hong Kong, Nanjing and Guangzhou were also participating.

However, the official Earth Hour website appeared blocked in Beijing, Shanghai and Tianjin on Saturday afternoon.

In Hong Kong, officials were to suspend the nightly "Symphony of Lights," which beams lights and lasers into the sky from 44 buildings along Victoria Harbour.

In Thailand, Prime Minister Abhisit Vejjajiva was to shut off lights along Khao San Road, a neighbourhood of bars and outdoor cafes in Bangkok.

Lights were also set to dim at the Grand Palace and other monuments, as well as a number of local businesses.

Bangkok had hoped to reduce electricity consumption by at least 30 per cent, or 1,400 megawatts. However, Earth Hour organizers say it is impossible to measure how much energy is saved worldwide.

With files from The Canadian Press and The Associated Press