A ventilation shaft at the Pike River Coal mine on the West Coast remains uncapped after toxic gases hampered efforts to seal the mine on Wednesday.
Twenty-nine workers were killed following a series of explosions at the mine near Greymouth which began on 19 November.
The officer in charge of the recovery operation Superintendent Gary Knowles says while there is no longer a flame in the shaft, it is still pumping out methane and other gases which are extremely volatile and dangerous.
Mr Knowles says the shaft is being monitored morning and night and it will not be capped until it is safe to do so.
A GAG machine designed to make the mine safe to enter is continuing to be used at the mine and is functioning well.