A marathon effort to retrieve the remains of 29 miners killed more than a decade ago in one of New Zealand's worst industrial accidents was called off Wednesday after workers found their path blocked by a tunnel collapse.

The miners died at the South Island's Pike River pit in November 2010 after a blast triggered by a build-up of flammable methane gas.

The government at the time promised to retrieve the entombed remains but suspended operations due to fears of further explosions, angering families of victims.

The controversy was so intense that Prime Minister Jacinda Ardern made restarting the recovery effort part of the campaign platform that saw her win office in 2017.

The Pike River Recovery Agency said Wednesday that workers had made their way 2.3-kilometres (1.4-miles) along the mine access shaft, or drift.

But it said the tunnel's roof had collapsed during the original disaster, preventing them advancing to the area where the miners' bodies most likely lie -- if they were not destroyed in the blast.

"Breaking through to the end of the drift was monumental," agency chief operating officer Dinghy Pattinson said in a statement.

"The boys and I feel pretty good to have now got as far as we can in the drift."

Those killed in the disaster included 24 New Zealanders, two Australians, two Britons and a South African.

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 managers.

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