It is the first time they have gone back into the mine since a series of explosions starting on November 19 killed 29 men, trapping their bodies 2.5 kilometres underground.
Three teams, each wearing breathing gear and working in two hour blocks, began surveying and checking gas levels today as they started setting up a new seal 168 metres in from the entrance, statutory mine manager Steve Ellis told NZPA.
"It went very well, the conditions were favourable this morning."
It took them a little longer to enter the mine than expected because "of the fantastic job of concreting the doors up".
The first team entered the mine about 11.45am to mark where everything was going.
The second team installed gas monitoring systems and prepared the site for the seal, while the third team, due to enter the mine about 5pm, would be transporting materials in.
When the sealed doors were opened up they saw exactly what was expected, Mr Ellis said.
"We've got lots of video footage from the robots... so there were no surprises in there."
However, "eerily" there was not a great deal of evidence of an explosion, he said.
"Pipes are in place, one or two cables had come away from the roof, but other than that, exactly as we expected."
Mr Ellis said it was hoped the pumping of a compound like expanding foam would start either late tomorrow or early Thursday.
They would then withdraw from the mine and monitor it for a week or two.
Eventually a steel door would be installed in the seal and the plan was then to remove the old seal at the mine entrance, a shipping container embedded in concrete installed just after the explosions.
The miners' families have been warned the rescue mission would be difficult and could take up to two years.
Prime Minister John Key said the Government's view was when it was safe to enter the mine "then that would be a welcome thing".
"We understand the stress that those families have been suffering and the very strong desire they have for recovery of their loved ones.
"My view's always been we couldn't put at risk the lives of those going to undertake that recovery effort, but that's a matter for others to determine whether actually this is the appropriate time.
"Clearly they feel it is and therefore we ultimately and fully support them in doing that but I'm not in a position to judge when it's safe to enter a mine or not."
Greymouth mayor Tony Kokshoorn said the plan to re-enter the mine was a "real confidence booster" for Greymouth.
"This is a big step forward, we've been waiting now with the families for seven months and it's been a hard, hard seven months.
"We are finally on the journey and this journey won't end until we recover the bodies to the families so we can have final closure."
He said the community knew there would be obstacles ahead.
