The four mines investigated on the west coast of New Zealand could all improve their safety procedures, including installing gas monitoring systems, according to the audit, which was released today.

The audits found two smaller mines, Roa and Burkes Creek, did not fully comply with the NZ Health and Safety in Employment Act.

At Roa, a high-level risk assessment was needed to identify all potentially fatal hazards, the auditors said.

Miner Bernard Green was killed in a rock fall at Roa in 2006.

The audit report recommended undertaking further geotechnical surveys at Roa to ensure mining practices were appropriate and that health and safety standards were followed and documentation was maintained to allow regular audits.

At Burkes Creek the auditors recommended the operators update and improve their mine plans, install an underground communications system, implement daily monitoring of the surface fan, and obtain a test certificate for explosives storage.

The Spring Creek and Huntly East mines owned by Solid Energy – which is hoping to buy the Pike River mine from the receivers – were also in need of improvements, although they complied with health and safety standards, the audit found.

At the Spring Creek mine the auditors identified a number of potential hazards, including the propensity for spontaneous combustion of the seam being worked and the presence of methane as a seam gas.

The audit report recommended establishing a management-wide internal audit system and a review of the responsibilities of the management team.

Spring Creek commissioned a review of the risk of underground explosion following the Pike River tragedy.

For Huntly East, the audit acknowledged Solid Energy already had significant documented systems in place but recommended it conduct a review of the document control process.

NZ Minister of Labour Kate Wilkinson said the audits found mine owners should enhance systems for identifying and mitigating hazards in each of the mines.

She said while the lack of imminent danger at the mines was reassuring, the government welcomed the recommended improvements.

"The auditors' recommendations do not indicate that the mines are being operated in an unsafe manner," she reportedly told the National Business Review.

"However, underground coal mining is inherently dangerous and the hazards cannot be entirely eliminated, so systems and processes to minimise harm must be in place."