Tianwan nuclear plant, the biggest joint investment between China and Russia, has connected its first reactor with the national grid, the China National Nuclear Corp (CNNC) announced on Saturday.

Two reactors have been planned for the nuclear plant in eastern Jiangsu Province, and when both are connected they will increase China's nuclear power output by as much as 30 per cent.

"The Tianwan project is the largest Sino-Russian joint investment in the technology and business field, and marks a new start for the two countries to work together for peaceful utilization of nuclear energy," Beijing-based nuclear builder CNNC said in a statement.

The first reactor is expected to begin commercial operations later this year, and the second should be connected with the national grid by the year-end, the company said.

Each has an installed capacity of 1,060 MW (megawatts), together boosting the country's nuclear capacity to 8,707 MW from the current 6,587 MW, according to statistics from CNNC.

The plant uses Russian pressurized-water technology, and has cost 26.5 billion yuan (US$3.3 billion) since construction began in October 1999.

China is working hard to diversify its energy mix to reduce its heavy reliance on air-polluting coal and high-priced oil. This effort involves pushing the use of nuclear energy and renewable sources such as wind and solar power.

The world's second-biggest energy consumer after the United States, China is aiming to increase the contribution of nuclear energy to 4 per cent of the country's electricity demand by the year 2020, from the current level of less than 2 per cent.