Czech Finance Minister Miroslav Kalousek voiced doubt on Friday about the cost of expanding the Temelin nuclear plant, a multi-billion project which has drawn bids from US and Russian groups.

"I don't have the right to say we'll put Temelin off...but to sign something this huge, I'd have to be sure the investment is efficient," Kalousek told the Hospodarske noviny business daily in an interview.

"And I'm not sure about that at all," he said, adding the plan for two new units was originally "calculated on the basis of much higher power prices than the current level."

The winner of the contract worth an estimated 200 to 300 billion koruna (8 to 12 billion euros, $10 to 15 billion) is to be announced this autumn.

US industrial giant Westinghouse is up against the MIR-1200 consortium, made up of Russia's Atomstroiexport and Gidropress and the Czech Skoda JS. France's Areva was eliminated from the running in October but has appealed against the decision.

"I must say the amount of the offers from both bidders was a very unpleasant surprise," Kalousek added.

CEZ, the Czech state-run power group which runs Temelin and is Central Europe's biggest utility, could reject both bids, Hospodarske noviny said.

But austerity-minded Czech Prime Minister Petr Necas insisted that the planned two new units were vital to industry as coal-fired plants are likely to be shut down by 2020 under the EU rules.

"This is a strategic decision that cannot be judged on the basis of its impact in the next year or two," Necas, a physicist and atomic energy advocate, told reporters as he toured Temelin on Friday.

The new units due to come online in 2025 aim to raise the share of nuclear power in the Czech energy mix to 50 percent from the current 30 percent.

Planned in the communist era and launched in 2000, the Temelin facility has been repeatedly criticised by Austria regarding safety concerns.