Aslan King, 25, was camping with friends near Princetown, Victoria, when he hit his head at around 2am on Saturday.
He reportedly got up suddenly and ran from the camping area into surrounding bushland.
His friends searched but have been unable to find him.
He is described as medium build with short dark hair. He was wearing a grey tracksuit and hoodie and may have blood on his forehead.
The Foreign Office said in a statement: “Our staff are seeking further information following the disappearance of a British man near Princetown, Australia and are in contact with the Australian police.”
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