TOKYO, Feb 14 (Reuters) - In a world first, Japan auctioned sovereign climate transition bonds on Wednesday although the bonds met with slightly weaker-than-expected demand.

Climate transition bonds are a relatively new class of bonds which aim to fund shifts by companies, or in this case a government, to having a lesser impact on the environment. They are distinct from green bonds where the proceeds are earmarked for a specific project or are focused on the profile of the issuer.

The sale of 800 billion yen ($5.3 billion) in 10-year transition bonds was the first in Prime Minister Fumio Kishida's plan to sell 20 trillion yen of climate bonds over the next decade to help the nation with its goal of cutting greenhouse gases to zero by 2050.

The proceeds are expected to go towards projects such as low-cost wind power generators and airplanes that use alternative fuels.

The bonds were priced to yield 0.74% on Wednesday, with pricing somewhat lower than expected. Yields on the bonds were 0.655% a day earlier in the so-called "when-issued" market, which is a market for securities yet to be issued. Yields on bonds move inversely to prices.

"I would say expectations prior to the auction were too high. Still the yield on climate bonds was little lower than the yield for 10-year JGBs, which means the bonds enjoyed a premium," said Keisuke Tsuruta, a fixed income strategist at Mitsubishi UFJ Morgan Stanley Securities.

Regular 10-year Japanese government bonds were yielding 0.755% on Wednesday.

Japan's finance ministry plans to sell 800 billion yen of five-year transition bonds on Feb. 27, which will be followed by 1.4 trillion yen of transition bonds in the fiscal year starting in April. ($1 = 150.52 yen) (Reporting by Junko Fujita; Editing by Edwina Gibbs)