State-run power giant CEZ on Monday formally asked three selected bidders to submit offers by July 2012 to build two new reactors at the Temelin nuclear power station in the southern Czech Republic.

"We expect high-quality bids from the selected bidders by July 2," CEZ chief executive and chairman Daniel Benes told reporters.

US energy giant Westinghouse, Russia's Atomstroiexport and France's Areva are bidding for the contract, estimated to be worth 20 billion euros ($28 billion).

"The development of nuclear energy and the completion of Temelin is one of CEZ's foremost strategic goals," Benes said.

CEZ, Europe's second largest power exporter, expects to announce the winner of the tender in 2013, and to launch the two new units at Temelin around 2025.

Benes said the documents handed over to the bidders on Monday comprised 6,000 pages weighing 70 kilos for two gigabytes of data.

Thomas Epron of Areva told AFP his group was the only bidder with experience building plants in Europe, namely in Finland and France.

"This is a competitive advantage... a factor that puts us in a particularly favourable position," he said, adding another advantage was a powerful and safe reactor of the EPR type.

Anders Jackson, Westinghouse's regional president, said the firm could offer technology that will make the plant very simple to operate, which "will also turn out to be very competitive in price."

Besides, "all our eight projects going on right now are on schedule and this is maybe the most important thing, to be able to deliver on schedule, on target," he added.

Planned in the communist era and launched in 2000, the existing Temelin facility includes two Russian-type VVER pressurised-water reactors, each with an output of 1,000 megawatts, made by Czech company Skoda Plzen and equipped by Westinghouse.

CEZ also runs the nuclear power plant in Dukovany in the southeast of the country, which together with Temelin produces one-third of the total Czech power output.

After the two units are built at Temelin, which lies about 120 kilometres (75 miles) south of Prague, the share of nuclear power is expected to rise to 50 percent of output.

"The construction of the two new units at Temelin is part of the Czech Republic's long-term energy strategy," Industry Minister Martin Kocourek said Monday.

Besides the expansion of Temelin and the potential construction of a new unit at Dukovany, the Czech government has mentioned the possibility of building a third nuclear plant in Blahutovice in the northeast of the country around 2040.