Origin Energy has advised the Australian Stock Exchange that Eraring Power Station in NSW's Hunter region is running out of coal.
The news resulted in the company slashing the profit target for the electricity business. It also threatens to deepen a worsening energy crisis engulfing Australia's east coast.
The company cited challenges, which it said had "deteriorated significantly" over recent weeks, in sourcing black coal for the 2880-megawatt generator.
Production issues at its primary supplier Centennial Coal's nearby Mandalong mine in NSW's Hunter region are not expected to ease until next year.
The company is seeking to source more expensive alternative supplies of the fossil fuel by rail.
Coal prices have been rising sharply as an energy crunch is being exacerbated by utilities shunning Russian supplies and scrambling for alternatives in a bid to starve Moscow of the revenue it needs to fund the war in Ukraine.
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"There is currently extreme volatility across commodity markets, driven by a combination of global energy supply and security concerns, exacerbated by the impact of the Russian invasion of Ukraine, with subsequent unprecedented increases in international energy prices including coal, gas and oil," Origin Energy said.
"Domestically, coal plant outages and high coal and gas prices have contributed to a steep escalation in wholesale electricity prices."
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