Two million residents, as well as businesses and government offices, are being urged to switch off non-essential lights at 7:00 pm (1200 GMT) to alert Thais to the ill-effects of climate change.

The city's Khao San road backpacker district, the downtown Silom business area and the neon-lit avenues of Chinatown are among the sections of Bangkok expected to be plunged into darkness.

Bangkok, with a total population of some 12 million people, spews more than 26 million tonnes of carbon dioxide into the air each year, or nearly 20 percent of Thailand's total CO2 emissions.

Street lights and other security-related lighting will remain on in a bid to thwart possible attacks, with Bangkok still on edge after deadly bombings on New Year's Eve and a small blast last weekend, governor Apirak Kosayodhin said.

"Only non-essential lights need be turned off," he told the Bangkok Post.

"These include billboard lights, decorative lighting at department stores and in shopfront windows, and some lights in households. There will also be extra police on duty to prevent crime," he said.

The lights-out campaign will include a public screening in a downtown shopping district of the Oscar-winning documentary "An Inconvenient Truth" by former US vice president Al Gore.