It wants to be able to increase tonnage trucked by 60 per cent to a total of 500,000 tonnes a year, up to the end of 2020. Daily truck movements would increase from 25 to 40, each way.

"If left unmitigated, onsite stockpiles at [Mt Piper] will continue to decline with potential impacts to the efficient operation [of the plant] and the supply of electricity to NSW," a statement from Centennial said.

Deputy Premier John Barilaro said a plan to increase trucked coal from the Clarence mine by 100,000 tonnes a year is open for public comment until June 20.

"Any short-term and long-term coal supply options to supply coal to the power station would require planning approval, and be subject to a comprehensive environmental assessment against the triple bottom line in accordance with existing government legislation, policy and guidelines," he said.

The NSW Nature Conservation Council said it was "very concerned about the impact of heavy diesel truck movements, mining and coal-fired power on air pollution and the health of residents in Lithgow and surrounding areas".

"In comparable regions such as Muswellbrook and Singleton, near the Bayswater and Liddell
coal-fired power stations and Hunter coal mines, or Stockton at the Port of Newcastle,
publicly available data shows these areas regularly breach national air-quality standards for
fine particles," it said.

Any approval of the additional trucking should be accompanied by the installation of at least two continuous air-quality monitoring stations in the Lithgow area, the council said.

A spokeswoman for Centennial said the trucking extension to the end of next year should "be sufficient" to meet the coal shortfall.

"We will also be seeking other ways, at our other sites, to provide future supply flexibility," she said.

EnergyAustralia said sourcing coal from the Lithgow region for its plant was the "preferred option".

Still, with the coal supply difficulties, the company needed to consider alternative supplies.

"We are exploring long-term approaches, including a rail uploader at Mt Piper to enable transporting coal from other regions in NSW," the EnergyAustralia spokesman, said.

Coal transport by road would avoid the town of Lithgow itself. The Herald also sought comment from Lithgow Council.