For more than half a century, the Liddell Power Station in the NSW Hunter Valley has burnt coal to power homes and industries.
AGL shutting down the first of four turbines, signalling the beginning of the end of the plant.
Today's switch-off has been a long time coming after AGL announced the retirement of Liddell in 2015.
The remaining units will continue to operate for another year until Liddell's full closure in April 2023.
AGL chief operating officer Markus Brokhof says the closure of Unit 3 is a significant moment in AGL's energy transition.
In 2015, the retirement of Liddell was announced, according to Brokhof.
We are pleased to be able to begin the orderly and responsible closure of the power station seven years later, in line with our climate commitments. AGL believes that the unit closure will result in a reduction in greenhouse gas emissions equivalent to taking about 400,000 cars off the road.
He said that was a good reduction of emissions.
Liddell opened in 1971 and was the most powerful generating station in Australia at one point.
Liddell is currently at zero for the Hunter Energy Hub site, which will house a grid-scale battery, solar thermal storage, wind, hydrogen and pumped hydro.
Mr Brokhof said planning was well underway to make sure there would be no power shortage as a result of Liddell's closure.
He said we believe that Liddell will not be a problem with his retirement from service and that we made this announcement early enough.
It will be a staggered approach. Green groups welcomed the first phase of the shutdown of Liddell.
Brad Smith of the Nature Conservation Council NSW said that retiring the Liddell plant would improve air quality for residents of the Upper Hunter.
There is still a long way to go, but this is a good start. AGL has announced that it will close its remaining coal-fired power stations with Bayswater shutting down between 2030 and 33 and Loy Yang A in Victoria between 2040 and 45.