Toyota Motor Corp is preparing to ramp up production of the hot-selling Prius hybrid by adding weekend shifts, and denied a report that it was considering building the model at a plant in California held jointly with General Motors Corp.

Citing two people familiar with the plan, Bloomberg News said on Wednesday Toyota was considering making the Prius at the joint Nummi factory after it had indefinitely postponed the start of planned Prius production at a half-built factory in Mississippi.

We are planning to produce the Prius at the Mississippi plant once the U.S. market recovers, and we are not considering production at Nummi, a Toyota spokeswoman said. The fate of the Nummi factory, held 50 percent each by Toyota and GM, has been called into question after the U.S. automaker filed for bankruptcy protection this month. The majority of the plant's production is already used for Toyota. GM produces one model, the Pontiac Vibe, and that brand is due to be discontinued next year.

Toyota builds the Prius at its Tsutsumi factory and another plant at affiliate Toyota Auto Body. The two Japanese plants are building the Prius at a combined pace of about 2,300 a day including overtime.

An executive said earlier this month Toyota was planning to start weekend shifts to meet demand for the Prius.

An official at Toyota Auto Body said the Prius now accounts for just under 30 percent of production at its Fujimatsu factory, adding the plant was considering adding weekend shifts in July.

The third-generation Prius became Japan's best-selling car after its debut in May, with sales of almost 11,000 cars.

(Reporting by Chang-Ran Kim; Editing by Michael Watson)

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