China has commercially started the first unit of its Tianwan nuclear plant in Jiangsu Province.

It is regarded as a major step forward in strengthening energy supply to the east.

The nation's top nuclear reactor builder, China National Nuclear Corp, said Monday that the reactor at the Tianwan Nuclear Station had generated 2.4 million megawatt-hours of electricity by May 17, which marked the start of commercial operation.

The unit, with generating capacity of 1,060MW, is equal to 15 percent of China's total nuclear capacity of about seven gigawatts from its existing nine nuclear units under commercial operation.

It is one of two units with same capacity planned for the first-phase development in the Tianwan project which started in 1999. They use technology from Russia's ZAO Atomstroyexport. The second unit is set to start commercially by the end of the year.

"The Tianwan nuclear project is the largest Sino-Russia technology economics cooperation project by far," CNNC, which holds 50 percent in the project, said in a statement. "These units are also the largest in terms of capacity across the country."

Among other shareholders, China Power Investment Corp has a 30 percent stake in the Tianwan project and a local asset management group holds the balance.

Under state plans, China wants to have 40GW of nuclear energy capacity by 2020, implying an average addition of 2GW per year.

But nuclear will remain a supplementary source of power production in China because of factors such as a shortage of uranium and the hefty cost in waste treatment, industry officials have said.