Police will not enter the Pike River mine until the entrance is entirely accessible, unless critical evidence is found and it is safe to do so.
The entrance of the Pike River coal mine where 29 men were killed by an explosion. Photo: petervick167/123RF
Police said their decision had approval from the Pike River Recovery Agency (PRRA) and WorkSafe and comes after careful discussion with experts.
Assistant Commissioner Tusha Penny said it was the safest way forward, and consistent with best practice for any forensic scene examination.
In a statement, she said the forensic examination was important, but the safety of all involved took precedence.
"Once the drift is fully recovered we will have a much better understanding of the environment inside the mine, and be in the best position to make informed decisions about our own staff entering the drift."
If police staff are not deployed early in the event of a critical find, then underground PRRA staff will be fully briefed and supported by police specialists above ground to undertake any essential forensic measures required.
Police have already been delivering forensic awareness training to PRRA mines staff this week, including scene examination, search techniques, forensic imagery, the management of exhibits and Disaster Victim Identification processes.
The government announced in November that the Pike River Mine would be re-entered, and the agency is currently timing the operation no earlier than the end of February.
Entering the 2.3km drift access tunnel is estimated to cost $36 million.
PRRA has given itself until June 2020 to complete the exhaustive work of safely re-entering the mine and properly investigating what has gone on inside.