Work on a gradual re-entry of the Pike River mine has been put back by at least a week due to a rise in carbon monoxide levels.
On Monday, key parties involved in the disaster agreed to a feasibility study for going underground to recover 29 men killed in explosions in November last year.
The company that owns the West Coast mine, Pike River Coal Ltd, was put in receivership in December.
The Mines Rescue Service was due to start work next Monday.
However, receiver John Fisk says a spike in carbon monoxide levels on Thursday has made the mine too dangerous to enter.
The situation will be reviewed next week.