All 29 miners trapped in a New Zealand mine after an explosion are presumed dead after a second blast occurred, rescuers said.

The workers - who include two Scottish men - could not have survived the "horrific" second explosion and rescue teams were "now in recovery mode", police said.

Pete Rodger, 40, from Perthshire, and Malcolm Campbell, 25, from St Andrews, Fife, were among the men missing following Friday's initial blast at Pike River mine in Atarau on South Island.

Superintendent Gary Knowles said: "Today there was another massive explosion underground and based on that explosion no-one would have survived. We are now in recovery mode."

Family members started shouting and fell to the floor after they were told, one witness said. TV footage at the scene showed relatives in tears and hugging each other.

Rescue teams had been unable to go into the mine after Friday's first blast because of high levels of toxic gases. Pike River mine chief executive Peter Whittall said the rescue teams were not doing anything that could have triggered the second blast.

A shaken Mr Whittall said: "I have met with the families and as you imagine they are absolutely devastated. They have all held out hope that it is their son, their husband, their brother would be the lucky one. I would have to say they are all probable feeling that hope's gone."

The country's Prime Minister John Key said New Zealand was "a nation in mourning". He passed on heartfelt sympathies to the families of the 29 victims: "After days of waiting and preparing for the worst and hoping for the best, they have been delivered the cruellest of news."

Mr Campbell had worked at the mine for two years and was due to marry his fiancee Amanda Shields, 23, on December 18. His parents Malcolm and Jane Campbell last week spoke of their hopes for their son, saying: "We can`t concentrate on anything, we can't sleep because it's difficult."

Former Perth Grammar pupil Mr Rodger, who previously worked on oil rigs, moved to New Zealand two years ago to be near his mother and sister who emigrated there. His New Zealand-born girlfriend Dianne Morris wrote on her Facebook site last week: "Just got to keep having positive thoughts."