The Pike River Coal mine on the West Coast has experienced a series of delays, equipment failures and a rock collapse in the ventilation shaft during its two-year life.
Rescue teams could be in a race against time to bring out 29 workers who have been trapped in the mine since Friday afternoon.
Radio New Zealand's environment reporter visited the South Island mine earlier this year and explains the risks:
The mine is not like the copper and gold mine in Chile which collapsed in August, leaving miners deep beneath the ground but in no immediate danger.
The Pike River Coal mine has been bored horizontally into the mountain side - meaning the rescue teams can walk in and the workers should be able to walk out.
But the danger is another methane gas explosion like that on Friday, which cut the power and blew out the ventilation fans.
The first 2km of the tunnel is in hard rock, which two miners who managed to get out on Friday say is not damaged.
But after that, the tunnels fan out into the coal seam where methane leaks out in dangerous quantities.
A team is analysing the gas and testing the air at the bottom of the pit before rescue teams can be safely sent in.
It could be that the 29 miners are fine and huddled around a fresh air source waiting for them. But if methane is building up from the coal seams, the situation will only become more dangerous.