An underground fire at a Hunter valley coal mine is a huge blow for mining giant Xstrata, which is already facing production setbacks due to flooding in Queensland. The fire broke out on Wednesday night, forcing the evacuation of the Blakefield South underground mine near Broke. 55 miners were safely brought to the surface and they have been stood down with pay while efforts continue to extinguish the fire. Xstrata spokesman, James Rickards says mining will not resume until it is safe to do so. "We are still trying to assess the full extent of the incident," he said. "The priority is that no one's underground, no one's been injured and we've been able to shut the operation down and now we're focussed on removing that fire from the situation." A cause for the fire has yet to be established but Xstrata says spontaneous combustion is one possibility. It is a huge setback for the mine which only commenced production at the end of last year as an extension of the Beltana operation.