TOKYO — Hydrogen-powered cars are finally being readied for their Prius moment — at least, that is what promoters of the environmentally friendly technology hope.

Toyota, maker of the Prius, the first hybrid vehicle to achieve mass-market acceptance, on Wednesday unveiled a concept version of a hydrogen fuel-cell car that it plans to begin selling “around 2015,” as the company put it. The bright blue sedan is shaped like a drop of water to emphasize that water is the only substance that hydrogen-powered cars emit from their tailpipes.

The car, which Toyota calls the FCV concept, was one of several vehicles with alternative powertrains to take the spotlight at the Tokyo Motor Show, which opened to reporters on Wednesday. Later in the day, two other carmakers, Honda and Hyundai, were expected to display new fuel-cell vehicles at a preview for the auto show in Los Angeles.

Honda was set to introduce a concept version of a new car it plans to introduce in 2015. Hyundai, which is based in South Korea, says it intended to beat both of its Japanese rivals to market next year with a hydrogen-powered vehicle based on its Tucson sport utility vehicle.