Safety experts have made what is being described as big headway in stabilising the shut-down Pike River mine.
Two trips were completed on Tuesday, marking the first time teams have entered the West Coast mine since explosions killed 29 men on 19 November last year. Their bodies remain in the mine.
Mines Rescue Service general manager Trevor Watts told Morning Report on Wednesday the work the men are doing at the moment is critical.
Mr Watts says the six-man teams travelled in 300 metres and found conditions were good. Gas monitoring equipment was installed and preparations begun for a concrete seal 170 metres inside the mine to keep out oxygen and prevent any further explosions.
Team members know what going back into the mine means for the families of the men killed and Tuesday was emotionally charged, he says.
On Wednesday, teams will go over data collected before heading back in for what is likely to be hard physical work.
The aim is to complete entry into the mine by stages over coming months, Mr Watts says.
