Twenty-nine people were killed at the Pike River mine in November 2010 after a blast triggered by a build-up of flammable methane gas.
The South Island mine has been sealed since amid fears of further explosions, angering family members who wanted the entombed remains recovered.
While some experts said the mine was too dangerous to enter, relatives of the victims argued it was the only way to find the cause of the blast that killed 24 New Zealanders, two Australians, two Britons and a South African.
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The controversy was so intense that when Prime Minister Jacinda Ardern was elected in 2017 she specifically appointed minister Andrew Little to oversee the mine's reopening.
Little announced on Wednesday that the seal to the Pike River mine access tunnel, or drift, had been opened as families of the dead looked on.
"Today we have returned," he said, describing the tragedy as "a consequence of corporate and regulatory failure".
"New Zealand is not a country where 29 people can die at work without real accountability... and that is why today we have fulfilled our promise."
Most of the bodies are believed to be near the end of the 2.3-kilometre long drift, although they may have been destroyed by the powerful explosion.
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Progress through the mine will be slow as workers attempt to minimise the risk of another methane explosion.
"However long that takes, the recovery project will be done professionally," he said.
"Most importantly, it will be done safely. Safety is the families' and the government's bottom line."
An official inquiry in 2012 criticised unsafe work practices at the mine and said it should never have been operating, although police said there was insufficient evidence to bring manslaughter charges against its managers.
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