International mine rescue experts say they are shocked a mining disaster the magnitude of the Pike River tragedy occurred in a modern mine.

International Mines Rescue Body secretary Alex Gryska said the world would be watching an investigation into the tragedy, which claimed the lives of 29 men.

Mr Gryska said he would not expect a disaster of that magnitude in New Zealand.

"Having incidents like this in developing countries is one thing. Having it happen in western countries is uncommon."

It is understood the disaster happened after a power cut stopped the Pike River ventilator shaft, increasing methane levels in the mine, he said.

Mr Gryska offered his organisation's resources and expertise to help the investigation into the disaster.

"It's a horrible event," he said. "When we have these kinds of occurrences we look at what's happened and we learn from it."

United Kingdom Mines Rescue operations manager Andrew Watson said safety alerts must have failed in the hours before the explosion at Pike River on Friday.

Methane levels have to reach five to 15 per cent of the atmosphere to cause a blast, he said.

Mr Watson said power went off in UK mines when methane reached 1.25 per cent and they were evacuated when it reached two per cent.

"So, either the warning system was inadequate, or it was not sufficiently monitored."

It was "shocking" that a tragedy the magnitude of the Pike River blast can happen in a modern mine, Mr Watson said.

Though he was not prepared to lay blame for the disaster, an investigation into what caused it would be closely analysed by international experts, he said.

"I've been in mines rescue for 32 years and I've never seen a disaster of this level. "The eyes of the world will be on this investigation."

The international mining community should band together to make sure safety standards are good for New Zealand miners, he said.

"This should never be repeated."