The price of liquefied natural gas in Asia has plunged by nearly half over the past five months—to the lowest level in more than three years—as Japan and South Korea have bought less and supplies have increased.

The Korea Gas Corp. liquefied natural gas terminal in Tongyeong, South Korea, in April. South Korea is one of the world's two biggest buyers of LNG. Bloomberg News

Dealers say the drop has forced some to sell shipments at a loss. Analysts say that if the price stays at current levels, Asian buyers may be less willing to commit to buying gas from planned billion-dollar export projects in the U.S., Canada and Australia.

South Korea and Japan are the world's two biggest buyers of LNG, natural gas that is super-chilled into liquid form for shipping and storage, but both countries have slowed buying.