Police are nearing the final stages in their criminal investigation into the first explosion at the Pike River Mine

29 miners were killed after the underground blast on the West Coast in November 2010.

Detective Superintendent Darryl Sweeney says this unique investigation is legally complex, and involved working alongside the Wellington Crown Solicitor for over a year.

He acknowledges this year will mark 16 years since the tragedy.

Sweeney says before any decisions can be made they'll be conducting a further investigation phase, with an update to come in several months.