The first trip into the Pike River coal mine since it was hit by a deadly explosion last November has been more productive than expected, a mine manager says.
A team of six New Zealand Mines Rescue workers entered the mine portal through a concrete air lock at its entrance this morning.
They carried out reconnaissance, before starting work on an air seal 168m into the mine this afternoon.
Statutory mine manager Steve Ellis said all the work so far had gone according to plan.
Teams had been able to carry in more building mateial into the mine than initally expected and were currently working to seal its portal, he said.
"The work has been a success."
Conditions inside the mine were as expected, with an air temperature of 12 degrees and an unbreathable atmosphere composed of 98 per cent nitrogen, Mr Ellis said.
He said six-strong teams could work a maximum of two hours in that environment before being replaced.
Those rotations would continue until the end of the week, when the 6.2m wide and 4.2m high concrete grout seal was expected to be finished, he said.
"It's like building a house slab but vertically. You'd be struggling to do that outdoors. It's a big job."
Once the first seal is complete, feasibility studies could be launched into how to recover the bodies of the 29 men still trapped inside the mine, Mr Ellis said.
He said seals could be made at different stages along the mine portal.
"This gives us a template that's repeatable. We can do a staged re-entry."
Those seals could be built anywhere up to 400m apart, he said.
"That's the kind of detail the study needs to investigate... It's not a quick fix."
Grey District Mayor Tony Kokshoorn earlier said today's operations have helped ease the disappointment of the last seven months waiting to get back into the mine.
"This is a new day. It's a all positive now. It feels like a new start.
"We've broke through now. We're not looking down a hole. We're in the hole."
Survivor goes back to mining
Meanwhile, one of the two survivors of the Pike River disaster has returned to coal mining in Australia after feeling a 'need' to go back to the profession he loves.
Daniel Rockhouse lost his brother Ben Rockhouse and 28 other co-workers in the explosion that hit the Pike River mine on November 19.
He was smashed into a wall by the force of the blast and had to recover from carbon monoxide poisoning before walking out of the mine.
His efforts to save fellow mine worker Russell Smith, who he found unconscious in the mine portal, saw him hailed as a hero.
Daniel's father Neville Rockhouse - the former safety and training manager at Pike River - said he was proud of his son for finding new work in a coal mine at Mackay in Queensland.
Despite all he had been through in the disaster, Daniel still felt a love for mining, Mr Rockhouse said.
"He said he needs to go back mining. 'I need to be back underground. I love it'."
Mr Rockhouse said he was not concerned about Daniel's decision.
Coal mining was not dangerous when its risks and hazards were well managed, he said.
"I'm very proud of him that he's done that.
"I just hope it goes well for him over there in Oz. A lot of people have the misconception that mining is a dangerous working environment. It's hazardous. Under normal circumstances we manage the hazards and risks quite adequately. No-one really knows yet what happened at Pike River."