Greymouth: Flags flew at half mast and church bells tolled across New Zealand on Thursday to mourn the country's worst mining disaster in nearly 70 years.

The government promised an independent inquiry into the tragedy in which 29 miners died after an explosion trapped them underground nearly a week ago at the Pike River Coal mine on the rugged west coast of the South Island.

"The country is unified in its grief and hopefully it will give some comfort to the families that have been left behind," Prime Minister John Key told Radio New Zealand, adding that an independent inquiry would be held in addition to probes by the Police, the Labour Department and Pike River Coal.

"We need answers to what happened at Pike River. We owe it to those families," Key told this small country of about four million people.

The New Zealand stock exchange opened the market five minutes late as a mark of respect for the disaster. Before the Ashes cricket test which started in Australia in Thursday, both teams observed a minute's silence in honour of the miners who included two Australians, two Britons and one South African.

New Zealand's rugby team has said they will wear white armbands as a mark of respect when the play Wales in a test match in Cardiff Saturday.

The 29 miners were trapped in the 2.3 km (1.4 mile) main tunnel last Friday night when methane gas caused a massive explosion in the mountain. Two other miners working away from the coal face narrowly escaped and walked out of the mine.

Wednesday, rescue teams had been readying to enter the mine and were reviewing deadly gas levels which had stopped them entering the mine, when the second gas explosion occurred.

The prime minister said a meeting with family members on Thursday contained "an awful lot of sorrow but not anger," and said the main priority was to see the men's bodies returned.

"I had quite a number of families come up to me and ask me to make sure we did everything we possibly could to make sure that their loved ones' could be removed, so they could have the appropriate funeral services," Key said.

Mine officials said the toxic gases which prevented rescue teams entering the mine, could delay retrieval of the bodies for possibly weeks or months.

"We have given an undertaking to the families that we will bring their boys back for them," mine chief Peter Whittall told a news conference Thursday.

"We need to make the place (mine) safe. We still can't send anyone underground. It will be days to weeks to get some closure for the families," said Whittall.

Whittall said the families did not want to seal the mine, making it a tomb for their husbands and sons.

Mine officials said they had made no decision on when or whether the mine would resume operations

The father of one of those killed, who had been outspoken about the way the rescue effort was handled, said he would not rest until he got answers.

"I'll make sure of that...it doesn't matter how long it takes, I'll get the truth," said Laurie Drew, father of 21-year-old miner Zen. Some relatives believed rescuers could have safely entered the mine after the initial explosion as the deadly toxic gases would have been consumed by the explosion.