ASTANA (Reuters) -Russia's state nuclear corporation Rosatom and state-owned China National Nuclear Corporation have been tapped to lead separate consortiums to build the first nuclear power plants in Kazakhstan, the country's atomic energy agency said on Saturday.

The oil- and gas-rich nation of 20 million has not had any nuclear power generation capacity since 1999, when the BN-350 reactor on the shores of the Caspian Sea was decommissioned.

Kazakhstan is one of the world's biggest uranium producers but currently relies mostly on coal-powered plants for its electricity, supplemented by some hydroelectric plants and the growing renewable energy sector.

In October, Kazakhstan voted in a referendum, backed by its president, in favour of constructing nuclear power plants. The country says it plans to have 2.4 gigawatts of nuclear capacity by 2035.

In a statement on Saturday, the Kazakh atomic energy agency, created this March, called Rosatom's proposal "the most optimal and advantageous", and said work has begun to attract state export financing from Russia.

Rosatom's chief executive officer Alexei Likhachev welcomed the news, saying that Rosatom's plant will be "based on the most advance and efficient design in the world."

The two-reactor plant will be built in the village of Ulken, about 250 miles (400 km) northwest of Almaty, the commercial capital. Likhachev said the plant would employ VVER-1200 Generation 3+ reactors, a Russian technology used both domestically and abroad.

Almasadam Satqaliev, the Kazakh agency's chairman, said Kazakhstan would sign a separate agreement with China's CNNC for a second nuclear plant.

"China is definitely one of the countries that has all the necessary technologies and the entire industrial base, and our next main priority is cooperation with China," Satqaliev said in a statement.

CNNC did not immediately reply to a request for comment outside of working hours.

It was not immediately clear which other companies would participate in the two consortiums, nor the cost and timeline of the proposals. French and South Korean companies had also submitted proposals to Kazakhstan.

Kazakhstan is boosting energy ties with both Russia and China. Russian President Vladimir Putin visited Kazakhstan in November to discuss energy and industry cooperation. The Central Asian country exports most of its oil through neighbour Russia, but is exploring alternatives.

China's top energy firm, China National Petroleum Corp, agreed in February with Kazakhstan's national gas company to take more gas for 2024-2025. It also signed a crude oil purchase and sales agreement with Tengizchevroil, a consortium producing oil in Kazakhstan.

(Reporting by Tamara Vaal in Astana; Additional reporting by Mariya Gordeyeva in Almaty and Ziyi Tang in Beijing; Writing by Lucy Papachristou in London; editing by Guy Faulconbridge and Toby Chopra)