The stabilisation process at the Pike River mine is expected to be completed in two weeks.
Twenty-nine men died in explosions at the West Coast coal mine in November last year, and their remains are yet to be recovered.
Statutory mine manager Stephen Ellis said on Tuesday that workers have removed the old portal seal that was established during the explosion and removed an old conveyor belt structure in 70 metres of the tunnel.
Mr Ellis says although there is little evidence of fire or explosion so far, there is some blackening of the strata in the mine.
He says installing air-lock doors, acting as a seal for the portal, is the last step before declaring the mine stable.
