GAG working to extinguish fire in Pike River mine.

Police have advised that the GAG unit, which is hoped will extinguish the fire in the Pike River coal mine, was successfully started at 10pm yesterday.

The jet engine has been operating all night and will continue until sampling indicates the fire has been extinguished and the atmosphere inside the mine is inert.

"This is a significant step forward," said Superintendent Gary Knowles.

"However, we are mindful that this is just a first step and we have a long way to go before the environment will be safe enough to send a recovery team into the mine."

Once the mine atmosphere is inert, work will start to cool the temperature inside the mine to enable the recovery team to enter. This is likely to involve pumping nitrogen into the mine.

Police do not yet have an indication how long this will take, however the mines experts warn it will not be a quick process.