The NSW mining watchdog is investigating after a worker died almost one kilometre underground in a "hot and humid" mine near Cobar.
The 36-year-old mobile rock drill operator reported feeling unwell while working alone 900 metres below the surface at the Peak Gold Mines on April 3, the state's Resources Regulator said in a statement on Wednesday.
The miner lost consciousness and stopped breathing while being driven to the surface by a co-worker. He was given CPR on the way but couldn't be resuscitated.
An initial investigation found the man's work environment was "hot and humid".
The regulator said the mine operator and contractor were co-operating with the investigation. The NSW coroner is also considering the cause of death.
© AAP 2017