The operation to re-enter New Zealand’s Pike river mine and recover the bodies of 29 miners killed in an explosion there nine years ago has begun, marking a “symbolic moment” more than two weeks after it was called off amid safety concerns.

The families of those killed were invited to a private event on Tuesday morning at the site on the South Island’s west coast to watch three experienced miners breach an 88cm concrete seal at the mine’s opening, enter and begin the $36m operation to find the bodies and work out what caused the explosion.

Pike River Recovery Agency (@PikeRecovery) Re-entry has happened! Dinghy, Kirk and Chris opened the doors and went inside, checked the drift condition, and then came back to a big cheer from the families.

Prime minister Jacinda Ardern said on Monday the re-entry would be a “symbolic moment” that would mark the start of an operation that could take “a number of weeks and months”. She has refused to specify when it would happen, preferring it to be kept between the families and the agency handling the operation. She said she would not attend the private event.

Pike river mine disaster: operation to retrieve bodies called off at last minute Read more

The earlier attempt, on 2 May, was a much more public affair but had to be called off at the last minute after inexplicably high oxygen levels were discovered in the mine. Minister Andrew Little said the presence of oxygen in a methane-producing environment carried the risk of explosion. The reason for the oxygen readings has since been pinned down to a leaking sample tube.

Facebook Twitter Pinterest Workers re-open the entrance to the Pike River mine, something the families of those who died in the explosion there have been calling for for years. Photograph: HANDOUT/AFP/Getty Images

The fatal explosion on 19 November 2010 has hung over the local community and grieving families seeking closure ever since the site was sealed off. It was the worst mine disaster in the country since 1914, claiming the lives of all of the men inside, including two Britons and two Australians.

Bernie and Kath Monk, who lost son Michael in the disaster, told the New Zealand Herald on Monday the families of victims had been invited to meet at 10am at the gate to the sealed-off mine. “We just got a message from the [Pike river recovery] agency … They are making it available for them to come up if they want to see the first wall taken out tomorrow, the 30-metre wall [30m inside the mine entrance].”

Asked if he was excited the re-entry was about to start, he said “Yeah I am. It’s something that should have been done eight years ago. History will be made tomorrow.”

Dave Gawnm the chief executive of the Pike river recovery agency, said they had completed preparations for the re-entry, including cutting through the concrete seal and ventilating the mine drift, or passageway.

Anna Osborne, who lost her husband to the mine explosion and is the chair of the group for the Pike families, told NZME that the event was “the start of a journey that will end with truth and justice”.

Facebook Twitter Pinterest Family members prepare to release 29 yellow balloons at the entrance to the Pike River Mine at a private family event ahead of body-recovery specialists entering the mine. Photograph: HANDOUT/AFP/Getty Images

“Watching those doors open and seeing the light enter that dark tunnel for the first time in years was incredibly emotional. We’ve known we are going back in for a year now, today it feels like it.”

Pike River Minister Andrew Little said there was still much to do while praising the families’ “tireless efforts” in their efforts for justice.

“New Zealand is not a country where 29 people can die at work without real accountability. That is not who we are. And that is why today we have fulfilled our promise.

“Today’s milestone belongs to the families and to the memory of their men. It also belongs to all New Zealanders, who know that going home to your loved ones is the least you should expect after a day’s work,” he said.

On Monday, Ardern said victims’ families – who have knowledge of mining – had understood the need for the delay earlier in the month. Anna Osborne lost her husband, Milton, in the disaster and said although the delay was “very disappointing” the families fully supported putting the health and safety of recovery workers first, because this was one of the lessons learnt from the mining disaster.

Facebook Twitter Pinterest A miners name tag board at the entrance to the Pike river coal mine. Photograph: Phil Walter/Getty Images

“We weren’t prepared for this but, that said, we always knew that things could change at the 11th hour,” said Osborne. “The mining industry is so changeable and unpredictable. We didn’t think anything would stop it going ahead this time but it has, and we have to accept that.”

Public pressure to launch an underground recovery mission has been intense since day one, spurred on by the astonishing rescue of 33 Chilean miners a few months before the explosion. But the John Key’s National government refused to budge, saying the mission was too complex and risky.

As part of her 2017 election bid, Ardern promised to re-enter the mine, with no less than two government ministers offering to be the first to set foot inside.