Underground workers at Pike River Mine have been removed from the job after carcinogens were detected in a tunnel.
Chief operating officer Dinghy Pattinson said an "unusual" substance was found on walls and the roof on the tunnel, and testing of samples discovered it was carcinogenic.
“As soon as we received notification back from our independent testing facility, we stopped work underground and withdrew the mine workers. We are now working with mining experts and WorkSafe to understand what the results of the testing mean for our operations.”
A risk assessment would now be carried out, and the Pike River Recovery Agency says it doesn't know how long it will take for workers to be allowed to head back in.
Last week, a 20-tonne loader was recovered from the mine.
Nearly 1600 metres of the 2300 drift has now been recovered.
Twenty-nine men lost their lives in an explosion in November 2010 at the mine, located on the West Coast.