New Zealand PM John Key says the country is standing shoulder to shoulder with the families who have lost loved ones .

There have been outbursts of grief and anger as the families of the 29 men who perished in the New Zealand mine disaster ask why more was not done to save their loved ones.

Anger in reaction to news of a second devastating blast this afternoon was directed at police, and things were on the verge of "turning ugly" during a private briefing for relatives.

One grieving father says heads should roll if it is found emergency crews could have acted sooner and saved their sons soon after the drama began unfolding on Friday.

The second blast ripped through the Pike River Mine around 2:30pm local time today, leaving authorities certain that the 29 miners trapped underground would have died.

For five days rescuers had been trying to reach them, but their efforts were continuously held back because authorities said the risk of poisonous gases and further explosions was too high to send them into the mine.

But families are demanding to know if there were earlier opportunities to launch a rescue bid, and if so, why this was not done.

New Zealand prime minister John Key has also signalled his cabinet is likely to set up an inquiry into the disaster on Monday.

Lawrie Drew's 21-year-old son, Zen, is among those who died in the disaster.

Mr Drew says families were inconsolable when they were told of the second explosion at a briefing this afternoon.

"They started the meeting off quietly, then everybody clapped and then we got this bombshell and people just erupted," he said.

"If it wasn't for the strong plain-clothes police and other police I think it could have got ugly."

Mr Drew says families thought they were about to get some good news.

"Well, we thought they were going in for a rescue mobilisation and we got told to hush up and then they told us a second explosion took place," he said.

"That's when people got up and started yelling abuse, saying 'you had the window of opportunity five days ago, why didn't you take it?'."

Mr Drew is calling for a Royal Commission into the deaths of his son and the other men.

"Coroners' reports - if they prove anyone was alive after that first blast, more heads are going to roll," he said.

"There should be a Royal inquiry, not a local inquiry from our New Zealand people. It's got to come from overseas from top people that know what they're doing."

abc.net.au