Disappointed investors in Sino Gas & Energy have accused the board of agreeing to a sale of at too low a price after US private equity giant Lone Star secured the directors' backing for a $530 million cash takeover offer without any formal search for a higher bid.

As Australia's only indigenous gas producer in China, Sino Gas, which started production in late 2014, is well placed to benefit from soaring demand for gas in one of the world's biggest energy markets.