The level of poisonous gas inside the Pike River mine has gone above the upper limit of monitoring equipment.
The plan for a gradual re-entry to the mine was delayed a second time this week because of an increase in carbon monoxide, due to more oxygen entering the mine because of weather cycles.
The families of the 29 men killed in explosions at the mine last November continue to push for the next stage of recovery to begin as soon as possible.
A lawyer for the families, Colin Smith, says the gas monitoring equipment at the mine site can measure only up to 1200 parts per million of carbon monoxide in the atmosphere, and the level has passed this.
Mr Smith says this means the monitoring teams cannot track the gas until it falls back below the equipment's limit.