A man had to be taken to hospital after his foot reportedly became caught in a strip conveyor at Appin mine.
The mine's owner, South32, confirmed a contractor sustained injuries to one of his feet while working underground at the mine on Saturday evening.
South32 said first aid was administered on site and the man was taken to hospital.
The Mercury has been told the man - whose age was not known - fell through safety mesh while undertaking cleaning operations and his foot was caught in a strip conveyor.
A company spokeswoman said: "The safety and well-being of our people is paramount at South32".
"The work area has been isolated and we are working with the [NSW Resources] Regulator to conduct a full investigation into the cause of the incident," she said.
"Our thoughts go out to our injured colleague and together with his employer we have offered our support."
It is understood the contractor was employed by Mastermyne Group.
The Mercury contacted the NSW Resources Regulator for comment.