State-owned electricity generator CS Energy says none of the 226 workers at the complex were hurt in the blaze which broke out in a cooling tower at the Callide C power station near Biloela, in central Queensland, on Monday.
The fire is the second industrial accident at the complex.
It comes 16 months after an explosion in a turbine hall knocked out the C4 generation unit back in May 2021.
CS Energy, which operates the Callide C plant as a joint venture with InterGen, says the damage and repairs are still being assessed.
It says the C3 unit will be taken offline until November 21, and potentially longer, as a precaution.
"The return to service date is based on the information that the JV has available at this point in time and may be subject to further change," CS Energy said in a statement.
That will effectively mean only two of the Callide power station's four generation units, which provide about 10 per cent of the state's generation capacity, will be operating for the next three weeks.
The May 2021 incident triggered an outage that affected more than 470,000 homes and businesses between the NSW border and Cape York.
CS Energy and InterGen initially forecast the C4 unit to be back online by June 2022, but said that date has been pushed back to April 2023.
"We will provide further updates as information becomes available," a CS Energy spokesperson said.
The B1 and B2 units at the neighbouring Callide B plant in the same complex were not affected by Monday's fire or the 2021 explosions and continue to operate.
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