Underground workers have been removed from the Pike River Mine following the discovery of a carcinogenic substance.
A recovery team working in the West Coast mine took samples after it found the "unusual" substance on the walls and roof of the tunnel.
The Pike River Recovery Agency says it's working with mining experts and WorkSafe to understand what the results mean for its operations.
A risk assessment is underway to look at the potential effects and ways to mitigate it, the agency says. It's unclear how long it will take.
"The reason we do all the tests we do and plan for every eventuality is so that we can take action when something like this occurs," agency chief operating officer Dinghy Pattinson says. "The health of all workers on site is always our top priority.
"We don't know yet how long it will take to ensure the environment underground is suitable for our workers - it will take as long as it needs to take."
It has been almost 10 years since the explosions in the mine killed 29 men.
