The $1 million sale of a coal-fired power station by the NSW government has been referred to the state's Auditor-General after it emerged the plant's new owners revalued it as being worth $730 million.

The Vales Point coal-fired power station was one of a number of power assets privatised by the then Michael Baird-run NSW government in late 2015.

The Vales Point power station, on the shores of Lake Macquarie, has been valued at more than 700 times the price at which it was sold. Credit:Wikimedia

It was bought by Sunset Power International for $1 million, a price which then treasurer – and now Premier – Gladys Berejiklian said was above its value.

Ms Berejiklian at the time said the sale would save the state from ongoing losses and liabilities associated with the plant's scheduled shut down in 2021. Ahead of the sale the state wrote down its value by more than $370 million.