The 29 miners trapped underground since an explosion at the Coal Pike Mine last week would have been unconscious before today's second explosion, a mining expert says.
Police have confirmed there was an explosion at the Pike River coal mine on the West Coast today, and they believe there is now no chance of any of the men surviving.
Families of the miners were told this afternoon there was an explosion at 2.37pm, and all hope was now lost.
Mine safety expert David Feickert said he had a message he hoped would give the families of the men some comfort.
"The chances are that the men became unconscious with carbon monoxide earlier on and they wouldn't have been affected by this explosion," he told TVNZ.
"The critical thing in terms of the 29 men was the carbon monoxide. ...
that is almost certainly what has killed them."
He was not surprised by the second explosion, saying it often happened in such situations and reinforced that the police had been right not to send rescuers in.
"Absolutely. They knew that this was very likely to happen because all of us in the industry follow what happens in gas explosions in coalmines around the world and there is a clear pattern of this kind of phenomenon," he said.
Air samples had showed there was heating going on, which would have been the coal seem burning or hot and debris from the first explosion smouldering. The ventilation was not working, which allowed the methane gas to accumulate.
"They're the two things you need to come together for another explosion," Mr Feickert said.
"That is what the rescue teams knew very well."