Fire crews are worried the huge amounts of water being used on a Victorian coal mine fire may affect the stability of the mine.
Fire Services Commissioner Craig Lapsley said there's been no movement that would compromise the mine but authorities need to be vigilant about the stability and integrity of the mine.
"What we've got is people working in a mine - if something was to move it compromises not only the integrity of the mine and the fire operation but it compromises firefighter safety," he said.
Mr Lapsley said the biggest challenge is the amount of water that's going in and coming out of the Hazelwood open-cut coal mine during the firefight.
"We are continually watching the stability of the mine and the amount of water that's in the mine," he told reporters in Morwell on Friday.
"Certainly we maintain water is the best weapon to put this fire out, and provided support with foams and different types of foams and wetting agents."
He said there's been no significant movement in the mine although there's been some small slips of coal, which he said was normal.
Mr Lapsley said authorities are talking to engineers about whether to dig or drill holes to get into parts of the mine.
Flooding the mine was not an option, he said.
"All the infrastructure would need to be taken out of the mine including the dredgers and it would take many, many months, if not years, to flood it."
The fire has been burning since February 9 in worked-out areas of the mine and is expected to run for at least another 10 days.
There was another fire in the Hazelwood mine in 2006 but Mr Lapsley said it was a different situation.
"We were successful in a matter of days to bring it to containment and a couple of weeks later the whole fire wrapped up," he said.
