The Minister responsible for Pike River re-entry has confirmed the date will be May 3.
Andrew Little said on Tuesday that since he announced on 14 November the project would proceed there has been an "incredible amount of preparation to get ready for re-entry".
"This has included preparing bridges for heavy loads, installing a nitrogen plant, upgrading the power supply, laying many kilometres of piping for the nitrogen, drilling more boreholes, installing monitoring equipment, and purging and ventilating the drift."
He said staff have been trained to work in a forensic environment, and Worksafe NZ have been "reviewing all aspects of the planning, risk assessments and supporting documentation, in order to ensure the re-entry plan is safe".
There is still more preparatory work to do, Mr Little said, including installing compressed air lines, awaiting the arrival of underground equipment, and breaching the concrete seal at 30 metres. Once the seal is breached the re-entry operation can begin.
"The re-entry will only take place if all the necessary pre-conditions have been met," he said, adding that an event will be organised at the site to mark the "important milestone".
"We're hopeful that work in the drift will enable the Agency and Police to thoroughly investigate what can be found there and find clues to what caused this dreadful tragedy," Mr Little said.
"This is about looking for clues to what caused the explosion that killed 29 men on 19 November 2010."