A "mega blaze" is believed to have destroyed several homes in the Hawkesbury area north-west of Sydney, where authorities issued an emergency warning.
Properties are believed to have been lost around Mt Tomah and Mt Wilson but there are no reports of injuries at this stage.
The fire was downgraded overnight to watch and act.
NSW Rural Fire Service (RFS) Deputy Commissioner Rob Rogers said there were reports properties were "impacted" after the fire grew "considerably" at its southern end over the afternoon.
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