Richard Ong's RRJ Capital and Temasek, Singapore's state investment agency, are investing about $600m to anchor Kunlun Energy's $1.35bn capital raising, two people familiar with the deal said.

Proceeds from the stock offer will go to the energy group's investment in liquefied natural gas. Kunlun Energy, a Hong Kong-listed unit of PetroChina, is among the Chinese companies spearheading the effort to reduce the mainland's dependence on coal and oil and switch to LNG, which is far cheaper than diesel and cleaner than coal.

The company plans to build 15 LNG plants, becoming China's largest onshore supplier. Given the enthusiasm for clean energy in China, the deal, which involved 800m primary shares at $13.10, or a 7.6 per cent discount to Monday's closing prices, was heavily oversubscribed, bankers say.

Breakthroughs in gas technology globally have upended the dynamics of the energy business, particularly in the US, where natural gas is now half the price of conventional diesel fuel. Coal prices have also fallen as many utilities plan to replace traditional fuel with LNG in new plants.

RRJ and Temasek have been big backers of the trend. Last year they combined forces to put $250m into Nasdaq-listed Clean Energy Fuels, a US-based group that provides natural gas fuel for transportation at gas stations in the US at a saving of $2 a gallon.

That transaction, which closed just three months ago, has already more than doubled in value. Kunlun Energy and Clean Energy Fuels have a similar mandate and Mr Ong hopes to bring the two together, according to one banker who worked on the deal.

"Richard has a knack for finding the right theme, finding the right assets and scaling the investment," the banker added. "Clean energy right now is a very powerful theme." RRJ Capital, which has more than $2.3bn under management, has always been close to Temasek.

At the beginning of the year Mr Ong's brother, Charles Ong, a senior managing director at the Singaporean investment firm, joined RRJ. The firm is currently planning a new $5bn fund, making it one of the most significant investors in the region.

In addition, key investors in the deal included CIC, China's sovereign wealth fund, which put in $50m and Petronas, the national oil company of Malaysia, which took a smaller stake.