Safety teams working at the Pike River coal mine had a slow start on Wednesday because of high atmospheric pressure outside.
Teams from the Mines Rescue Service entered the mine for a second day as they prepare the first of a series of new airtight seals.
Pike River's statutory mine manager Steve Ellis, says teams could not get into the mine until about midday because the high atmospheric pressure outside meant the mine was sucking in oxygen.
Mr Ellis says the teams had to make sure all sealing around the mine's portals was up to scratch so there was no danger of explosion inside.
But the teams are back inside, and have taken all the materials they need for the first double seal being installed at the 170-metre mark.
The seals are the first of many to be installed in steps of several hundred metres so recovery teams can make their way up the mine shaft safely.
They will be looking for the bodies of 29 men who died in a series of explosions at the mine last November.
Mr Ellis says high pressures are forecast until Saturday or Sunday and this could slow down the work.