The Pike River mine re-entry mission has been suspended by the coronavirus lockdown.

The Pike River Recovery Agency (PRRA), which has been working to try and recover the 29 men killed in the 2010 disaster, shut down the operation last week.

On the eve of the level 4 Covid-19 national lockdown, the agency's ventilation officer gave bosses two options on how the potentially-volatile mine could be managed: close and seal the emergency doors and fill the drift with nitrogen, or walk away and leave the mine in its current state.

The majority voted to leave the mine in its current state with the main fan running, the portal emergency doors open and one nitrogen compressor running, according to a letter to WorkSafe by chief operating officer Kevin "Dinghy" Pattinson, a fifth-generation West Coast miner.

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PRRA chief executive Dave Gawn told the Herald today: "The re-entry and recovery operation is being paused, in light of the Government directives concerning Covid-19 alert level 4, with a small group of technical staff continuing to monitor the drift daily via remote channels for safety and stability, as well as completing one weekly onsite inspection to assess conditions. We have been communicating with families throughout the lead-up to moving the mine into care and maintenance."

Nitrogen will still be pumped into the mine's drift to manage the risks of "an explosive mixture occurrence due to either methane expansion into the drift or fresh air migration into the mine" and the risk of "spontaneous combustion or rekindling risk inbye the plug due to fresh air migration through the plug".

"However, please note as a contingency that if, for whatever reason, we lose control of the atmosphere in the mine, we have the option to close the emergency doors at the portal, seal the door and fill the mine and drift with nitrogen," Pattinson says.

Covid19.govt.nz: The Government's official Covid-19 advisory website

The nitrogen plant will operate 24/7 under reduced capacity but Pattinson says ongoing inspections are needed to ensure the site's safety.

From Wednesday, weekly onsite inspections will begin, with a limited number of personnel travelling in their own vehicles to limit contact.

Remote daily monitoring will be carried out by the ventilation officer, geotechnical engineer and electrical superintendent.

All other non-essential staff needed to maintain the mine have been sent home to work remotely where possible.

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The PRRA operation is looking to see whether it can recover the 29 men killed during the November 19, 2010 disaster.

Expert miners had been working for months to purge methane and oxygen from the mine by pumping in nitrogen through pipes before they finally headed underground in May last year.

Progress has been slow and held up with unexpected delays.

Earlier this month, Pike River Recovery Minister Andrew Little approved a further $10.8 million funding to complete the project - as well as a $4.2m contingency – meaning the total operation could end up costing $51m. Its original budget was $23m.

The West Coast of the South Island had its first confirmed case of Covid-19 late last week – and yesterday it was confirmed that a woman in her 70s was the first person in New Zealand to die from the virus at Grey Base Hospital in Greymouth.