Prime Minister John Key says there will be an inquiry into the events at the Pike River Coal mine once the rescue operation has been completed.
Twenty-nine workers trapped underground have not been heard from since an explosion at the mine at Atarau on the West Coast on Friday afternoon.
Mr Key travelled to Greymouth on Monday to meet rescue workers and speak to the men's families. It is his second visit to the area since the explosion.
Mr Key says it is a testing and difficult time for the families, but they are aware of the safety issues involved with the rescue operation.
The union representing miners is calling for a public investigation into the explosion.
The Engineering, Printing and Manufacturing Union says right now the rescue effort must be the priority, but following that, a thorough inquiry will be required.
National secretary Andrew Little says the usual Department of Labour investigation will not be enough.
He would like to see a public hearing in front of a senior judge and top experts.
Mr Little says that is the only way to assure people every possible cause has been looked at.