Underground workers have been withdrawn from the Pike River Mine after samples returned positive for the presence of carcinogens.
The Pike River Recovery Agency says the team working underground have encountered an unusual substance on the walls and roof of the tunnel and took samples.
Police have also stopped their investigation into items recovered from the Pike River mine.
Police say their team has also stopped work at the site.
They say they're no longer handling any potential exhibits.
Last week, a loader driven by one of the two men to survive the Pike River Mine explosion 10 years ago was pulled out of the drift by the Pike River Recovery Agency underground team.
The loader was being driven by Russell Smith on November 19, 2010, when the mine exploded, killing 29 men.
The recovery team reached the machine at the 1575m mark, and removed it by pushing and pulling it with loaders on either side.
Minister Responsible for Pike River Re-entry Andrew Little, said the recovery meant they were now moving into an area of the Pike River Mine that had not been seen since the explosion.
"The fifth and last robot was recovered before the loader, and now there's several hundred metres of previously unexplored drift and roadways in the Pit Bottom in Stone area that have not been seen since 2010.
"We've reached a significant point in the recovery which is about trying to find out why the 29 men who went to work on 19 November, 2010 didn't come home."
The $51 million recovery is nearing the end of the drift (entry tunnel) and the project.