Echoing similar comments he made earlier this month, Rio Tinto Coal Australia managing director Chris Salisbury told the Newcastle Herald that the existing approvals only allowed for production until late 2015.

"We're now running out of time in what is an extremely challenging environment for the coal industry, where mines without a strong future are being shut down," he told the newspaper.

Rio subsidiary Coal & Allied is seeking approvals to continue operating the MTW complex until 2035 with the separate environmental impact statements for the Mount Thorley and Warkworth mines recently entering the public exhibition phase, which will end on August 6.

In the applications the company stressed the need to maintain existing production rates of 18 million tonnes per annum run-of-mine from the Warkworth mine and 10Mtpa ROM from Mount Thorley.

While the New South Wales Supreme Court upheld a Land and Environment Court decision to halt the extension project in April, the state government has since reportedly passed a planning policy that made the economic benefits the "primary consideration".

Overall RTCA claims the extension projects have net economic benefits of $1.5 billion and royalties of $617 million.